Prepared in cooperation with the New York State Department of Environmental Conservation

Effects of Recreational Flow Releases on Natural Resources 

of the Indian and Hudson Rivers in the Central Adirondack 

Mountains, New York, 2004–06

Scientific Investigations Report 2010–5223

U.S. Department of the Interior

U.S. Geological Survey
Cover. Main photograph—Hudson River near the Blue Ledges, October 2004.

 Inset photograph—Rafters at the confluence of the Indian and Hudson Rivers, July 2005.
Effects of Recreational Flow Releases 

on Natural Resources of the Indian and 

Hudson Rivers in the Central Adirondack 

Mountains, New York, 2004–06

Prepared in cooperation with the 

New York State Department of Environmental Conservation 

Scientific Investigations Report 2010–5223

U.S. Department of the Interior

U.S. Geological Survey

By B.P. Baldigo, C.I. Mulvihill, A.G. Ernst, and B.A. Biosvert
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2010

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Baldigo, B.P., Mulvihill, C.I., Ernst, A.G., and Boisvert, B.A., 2010, Effects of recreational flow releases on natural 

resources of the Indian and Hudson Rivers in the Central Adirondack Mountains, New York, 2004–06: U.S. Geological 

Survey Scientific Investigations Report 2010–5223, 72 p., at http://pubs.usgs.gov/sir/2010/5223.
iii

Acknowledgments

The authors extend their appreciation to Rick Preall, Rick Fenton, and Emily Zollweg of the 

New York State Department of Environmental Conservation; Cliff Kraft, Dan Josephson, Milo 

Richmond, Marshall Thomas, Mike Compton, Brittney Foster-Pettit, Ian Kiraly, Alexandra Denby, 

Theodore Treska, Madeleine Mineau, Geoff Steinhart, Beth Vollmer, David Post, Edward Camp, 

Francoise Vermeylen, Evan Cooch, Patrick Sullivan, Todd Walter, and Walter Keller of Cornell 

University; and Tom Coe and the staff at the Warrensburg Hatchery for their technical and field 

support. We also thank the many landowners along the Indian, Cedar, and Hudson Rivers for 

allowing access to their properties; these include, but are not limited to, The Gooley Club; Finch, 

Pruyn & Company, Inc.; The Barton Mine Company; Elva Brown; and Pat Cunningham. Additional 

thanks go to Justin Blanco, Doug Wells, Patrick Sista, Larry Ames, Jim Nash, Gregg Hogancamp, 

Wayne Failing, and Pete Burns. This research was supported by funds from the New York 

State Department of Environmental Conservation, the New York Cooperative Fish and Wildlife 

Research Unit, and the Kieckhefer Adirondack Fellowship.
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v

Contents

Executive Summary....................................................................................................................................xiii

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Measuring the Effects of Recreational Flow Releases on Habitat and Biological Communities.....3

Study Sites .............................................................................................................................................3

Stage, Discharge, and Water Temperature......................................................................................3

Stream Habitat.......................................................................................................................................4

Distribution of Wetlands ......................................................................................................................8

Temporal and Spatial Patterns in River Temperature.....................................................................9

Fish Communities .................................................................................................................................9

Macroinvertebrate Assemblages ......................................................................................................9

Monitoring Trout Behavior and Temperatures...............................................................................10

Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers..13

Discharge of the Indian River Below Lake Abanakee..................................................................15

River Temperatures ............................................................................................................................19

Temporal and Spatial Patterns in Temperature of the Hudson River ........................................22

River Habitat .......................................................................................................................................32

Distribution of Wetlands ...................................................................................................................32

Fish Communities................................................................................................................................36

Macroinvertebrate Assemblages ....................................................................................................45

Trout Behavior.....................................................................................................................................55

Summary........................................................................................................................................................69

River Discharge and Stage ...............................................................................................................69

River Temperatures ............................................................................................................................69

Lake Stage (Surface-Water Elevation) in Lake Abanakee...........................................................69

Stream Habitat ....................................................................................................................................69

Wetlands ..............................................................................................................................................69

Temporal and Spatial Patterns in River Temperatures.................................................................69

Fish Assemblages...............................................................................................................................70

Macroinvertebrate Communities .....................................................................................................70

Trout Telemetry....................................................................................................................................70

References Cited..........................................................................................................................................71

Figures

1. Map showing locations of study sites and dams on the Indian, Hudson, and Cedar

Rivers, Adirondack Mountains, New York................................................................................4

2. Aerial photograph of the Indian River from Abanakee Dam (lower left corner) to

downstream confluence with the Hudson River (upper right corner), Adirondack

Mountains, New York...................................................................................................................7

3. Map showing wetlands on sections of the Indian and Cedar Rivers, Adirondack

Mountains, New York...................................................................................................................8
vi

4. Graphs showing change in stage at three Indian River sites A, on July 7, 2005, a

release day, and B, on July 8, 2005, a nonrelease day, Adirondack Mountains, 

New York ......................................................................................................................................19

5. Graphs showing change in stage at five Hudson River sites A, on July 7, 2005, a

release day, and B, on July 8, 2005, a nonrelease day, Adirondack Mountains, 

NewYork .......................................................................................................................................19

6. Graph showing change in stage at eight study sites on the Hudson and Indian

Rivers, Adirondack Mountains, New York, on release and nonrelease days from

July 1 to August 1, 2005..............................................................................................................20

7. Graph showing lake stage at Lake Abanakee at Route 28 bridge near Indian Lake

(AB02), Adirondack Mountains, New York, during October 2005 .......................................21

8. Graph showing lake stage at Lake Abanakee at Route 28 bridge near Indian Lake

(AB02), Adirondack Mountains, New York, during June and July 2006 ............................21

9. Graph showing lake stage at Lake Abanakee at Route 28 bridge near Indian Lake

(AB02), Adirondack Mountains, New York, during August 2006.........................................22

10. Graphs showing stage at Indian Lake, Lake Abanakee (AB02), and Indian River

(IR01), Adirondack Mountains, New York, A, during July 2005, and 

B, during July 2006......................................................................................................................23

11. Graph showing change in temperature of the Indian River at three study sites in the

Adirondack Mountains, New York, from July 18 to July 21, 2005 .......................................26

12. Graph showing change in temperature of the Hudson River at four sites, in the

Adirondack Mountains, New York, from July 18 to July 21, 2005 .......................................26

13. Graph showing change in temperature at eight study sites on the Hudson and

Indian Rivers in the Adirondack Mountains, New York, on release and nonrelase

days from July 1 to August 1, 2005...........................................................................................27

14. Graphs showing longitudinal temperature profiles of the three Indian Rivers study

sites IR01–IR03, and Hudson River study sites HR02–HR05, in the Adirondack

Mountains, New York, at A, 10:12, B, 12:39, and C, 15:42 Eastern Standard Time

(EST) during release and nonrelease flows on Julyu 25, 2005; mean temperature at

thse seven study sites from July 21, 2005 through September 21, 2005, on release

and nonrelease days, and inflow points for five cool-water tributaries ...........................28

15. Map showing five tributaries entering the bottom third of the study reach at or

below the confluence of the Hudson River with the Boreas River, Adirondack

Mountains, New York.................................................................................................................36

16. False-color images of the confluences of Raquette Brook at kilometer 24 and 

Deer Creek at kilometer 27 with the Hudson River during flights at A,10:12, 

B, 12:39, and C, 15:42 Eastern Standard Time in the Adirondack Mountains, 

New York ......................................................................................................................................38

17. Graph showing estimates of density, biomass, and 95-percent confidence intervals

for fish communities surveyed at 11 study sites on the Indian, Hudson, and Cedar

Rivers, Adirondack Mountains, New York, 2005–2006..........................................................42

18. Graph showing diversity, equitability, richness, and dominance for fish communities

at 11 study sites in the Indian, Hudson, and Cedar Rivers, Adirondack Mountains,

New York, 2005–2006..................................................................................................................42

19. Graphs showing density (number of fish per 0.1 hectare) of each fish group or

species at 11 study sites on the Indian, Hudson, and Cedar Rivers, Adirondack

Mountains, New York, 2005–2006.............................................................................................45

20. Graphs showing biomass (grams per 0.1 hectare) of each fish or species at 

11 study sites on the Indian, Hudson, and Cedar Rivers, Adirondack Mountains, 

New York, 2005–2006..................................................................................................................47
vii

21. Graph showing Average New York State Bioassessment Profile scores and

95-percent confidence intervals for Fisher’s least significant difference in relation

to impact categories at 12 sites surveyed in the Indian, Hudson, and Cedar Rivers,

Adirondack Mountains, New York, August 2006 ...................................................................49

22. Graph showing the percentages of macroinvertebrates in each of five functional

feeding groups at 12 sites surveyed in the Indian, Hudson, and Cedar Rivers,

Adirondack Mountains, New York, August 2006 ...................................................................52

23. Graph showing cluster analysis of Bray-Curtis similarities for macroinvertebrate

assemblages based on square-root-transformed relative abundance data from 3

combined replicates collected at each of 12 sites in the Indian, Hudson, and Cedar

Rivers, Adirondack Mountains, New York, August 2006 ......................................................54

24. Diagram of ordination plot of macroinvertebrate assemblages based on

square-root-transformed relative abundance data from 3 combined replicates at

each of 12 sites in the Indian, Hudson, and Cedar Rivers, Adirondack Mountains,

New York, August 2006 ..............................................................................................................54

25. Graphs showing percentages of temperature differences that were greater than 

or equal to -1o Celsius on nonrelease days within time blocks TB1, TB2, and TB3 

in the A, Cedar River (2006), B, Indian River (2005–2006), and C, Hudson River

(2005–2006), Adirondack Mountains, New York ....................................................................57

26. Graphs showing percentages of temperature differences that were greater than 

or equal to -2 o Celsius on nonrelease and release days within time blocks TB1, 

TB2,and TB3 in the A, Cedar River (2006), B, Indian River (2005–2006), and 

C, Hudson River (2005–2006), Adirondack Mountains, New York.......................................57

27. Graphs showing average differences between trout and river temperatures and

standard errors for all observations of 17 trout tracked in the Hudson River,

Adirondack Mountains, New York, during 2006.....................................................................58

28. Graphs showing percentage of observations of trout temperature lower than 

20oCelsius on nonrelease and release days within time blocks TB1, TB2, and

 TB3 in the A, Cedar River (2006), B, Indian River (2005–2006), and C, Hudson River

(2005–2006), Adirondack Mountains, New York ....................................................................59

29. Graphs showing estimated least-square mean temperature differences and

standard errors calculated from the best supported multilevel model for the 

A, Cedar and B, Indian Rivers, Adirondack Mountains, New York, during the 

afternoon time block (TB3), and the C, Hudson River during the midday time 

block (TB2) during 2006..............................................................................................................60

30. Graphs showing percentage (and number) of trout temperatures that increased,

stayed the same, or decreased over the time span when release bubbles arrived at

the trout’s location on nonrelease, release, and flooding days in the A, Indian River

and B, Hudson River, Adirondack Mountains, New York, during 2006 ..............................62

31. Graphs showing dispersal of individual brown trout upstream (positive) and

downstream (negative) from stocking locations in the A, Cedar, B, Indian, and 

C, Hudson Rivers, Adirondack Mountains, New York, at approximately 1, 7, 30, and 

60 days after stocking during 2006...........................................................................................63

32. Graphs showing mean absolute distance (±2 × standard error) of all brown trout

from the stocking location in the A, Cedar, B, Indian, and C, Hudson Rivers,

Adirondack Mountains, New York, at approximately 1, 7, 30, and 60 days after

stocking during 2006...................................................................................................................64

33. Maps showing distribution of brown-trout observations in generalized study

reaches in the A, Cedar, B, Indian, and C, Hudson Rivers, Adirondack Mountains,

New York, during 2006................................................................................................................65
viii

34. Graphs showing summary of brown-trout activity (distance trout moved 

between consecutive days) in the Cedar, Indian, and Hudson Rivers, 

Adirondack Mountains, New York, during 2006.....................................................................67

35. Graphs showing persistence of brown trout (number of days trout were 

apparently alive and within the study reach) in the Cedar, Indian, and Hudson 

Rivers, Adirondack Mountains, New York, during A, 2005, and B, 2006 ............................67

36. Graphs showing the number of tagged trout apparently alive each day and with 

the study reach in the Indian and Hudson Rivers during 2005 and 2006 and in the 

Cedar River during 2006, Adirondack Mountains, New York...............................................68

37. Graphs showing confirmed or inferred final location of transmitters that had been

implanted into 75 brown trout and stocked into the Indian and Hudson Rivers

during 2005 and 2006 and into the Cedar River, Adirondack Mountains, New York,

during 2006...................................................................................................................................68

Tables

1. Characteristics of 14 study sites at Lake Abanakee and on the Indian, Hudson, and

Cedar Rivers in the Adirondack Mountains, New York, 2005 and 2006 ...............................5

2. Dates when data on river stage and temperature were collected at 10 study sites

on Lake Abanakee and the Indian and Hudson Rivers in 2005 and 2006.............................6

3. Examples of telemetry data logged for trout 151444 on given days and during

selected time blocks under release or nonrelease conditions in the Hudson River 

in June 2006 .................................................................................................................................14

4. The scope of the trout telemetry sampling effort in 2005 and 2006 ...................................15

5. Daily discharges in cubic feet per second on the Indian River below Lake

Abanakee near Indian Lake (site IR01) for November 2004 through September 

2005 and total monthly discharges with daily mean, maximum, and minimum for 

each month ..................................................................................................................................16

6. Daily discharges on the Indian River below Lake Abanakee near Indian Lake 

(site IR01) for October 2005 through September 2006 and total monthly mean 

discharges with daily mean, maximum, and minimum for each month ............................17

7. Mean change in river stage from start of release to peak flow on release days 

and during the same interval on nonrelease days and number of release and

nonrelease days at eight sites on the Indian and Hudson Rivers in the Adirondack

Mountains, New York, for each month during June–September, 2005 .............................18

8. Mean change in river stage from start of release to peak flow on release days 

and during the same interval on nonrelease days and number of release and

nonrelease days at eight sites on the Indian and Hudson Rivers in the Adirondack

Mountains, New York, for each month during June–September, 2006 .............................18

9. Mean change in the stage of Lake Abanakee from start of release until closing of

the spillway gate on release days and number of release and nonrelease days at

two study sites in the Adirondack Mountains, New York, and during the same

interval on nonrelease days during June–September 2005 and at one site during

June–September 2006 ...............................................................................................................20

10. Mean change in temperature from start of release to peak flow on release days

and during the same time period on nonrelease days and number of release and

nonrelease days at eight sites on the Indian and Hudson Rivers in the Adirondack

Mountains, New York, during June–September, 2005..........................................................24
ix

11. Mean change in temperature from start of release to peak flow on release days

and during the same time period on nonrelease days and number of release and

nonrelease days at eight sites on the Indian and Hudson Rivers in the Adirondack

Mountains, New York, during June–September, 2006..........................................................25

12. Median temperature for each 1-kilometer section and refuge areas 1, 2., and 

3oC below the median temperature for that section, during three flights along the

27-kilometer reach of the Indian and Hudson Rivers from the outflow point of the

Abanakee Dam to North Creek, Adirondack Mountains, New York, July 25, 2005..........29

13. Median temperature and refuge areas 1, 2, and 3°C below the median temperature

for unshaded halves of each 1-kilometer section divided along the thalweg along

the 27-kilometer reach of the Indian and Hudson Rivers from the outflow point of

the Abanakee Dam to North Creek, Adirondack Mountains, New York. ..........................33

14. Median temperature and refuge areas .5, 1, 1.5, and 2°C below the median

temperature for each 1-kilometer section along the 27-kilometer reach of the

Indian and Hudson Rivers from the outflow point of the Abanakee Dam to North

Creek, Adirondack Mountains, New York, 2005. Sections under the high-water

bubble are highlighted ...............................................................................................................37

15. Areal percentage of seven types of geomorphic channel units (GCUs) in the 

Indian River, Adirondack Mountains, New York, at base flow on August 4, 17, 

and 18, 2005, and the total area and number of GCUs mapped. ........................................39

16. Lengths and areas of wetlands along the Indian River and along surveyed 

sections of the upper and lower Cedar River, Adirondack Mountains, New York, 

2005, and the percentages of river length bordered by wetlands. ....................................41

17. Estimates of fish-community parameters for 11 study sites on the Indian, Hudson, 

and Cedar Rivers, Adirondack Mountains, NY, 2005 and 2006. ..........................................41

18. Estimates of density for each fish species collected at each of 11 study sites on 

the Indian, Hudson, and Cedar Rivers, Adirondack Mountains, New York, 

2005–2006 ....................................................................................................................................44

19. Estimates of biomass for each fish species collected at each of 11 study sites on 

the Indian, Hudson, and Cedar Rivers, Adirondack Mountains, NY, 2005–2006 ..............46

20. Mean estimates for macroinvertebrate community richness, Hilsenhoff’s Biotic 

Index, Ephemeroptera-Plecoptera-Trichoptera (EPT) richness, Percent Model Affinity 

(PMA), and the New York State Bioassessment Profile (NYSBAP) for 

samples collected in riffles at 12 study sites in the Cedar, Indian, and Hudson 

Rivers, Adirondack Mountains, New York, 2005–2006..........................................................48

21. Mean estimates for macroinvertebrate community richness, Hilsenhoff’s Biotic 

Index (HBI), Ephemeroptera-Plecoptera-Trichoptera (EPT) richness, Percent 

Model Affinity (PMA), and the New York State Bioassessment Profile (BAP) and 

similarities among 12 study sites in the Cedar, Indian, and Hudson Rivers, 

Adirondack Mountains, New York, 2006 .................................................................................50

22. Percentage compositions of five functional feeding groups in macroinvertebrate 

communities at 12 study sites in the Cedar, Indian, and Hudson Rivers, Adirondack 

Mountains, New York, 2005–2006.............................................................................................51

23. Mean percentages of macroinvertebrate community feeding groups and 

similarities among 12 study sites in the Cedar, Indian, and Hudson Rivers, 

Adirondack Mountains, New York, 2006 .................................................................................53
x

Conversion Factors, Datums, and Acronyms

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

hectare (ha) 0.003861 square mile (mi2) 

square kilometer (km2) 0.3861 square mile (mi2)

Volume

cubic meter (m3) 35.31 cubic foot (ft3)

Flow rate

cubic meter per second (m3/s) 35.31 cubic foot per second (ft3/s)

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 259.0 hectare (ha)

square mile (mi2) 2.590 square kilometer (km2) 

Volume

cubic foot (ft3) 0.02832 cubic meter (m3) 

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F= (1.8×°C) +32

24. Percentages of all morning, midday, and afternoon observations of trout body 

temperatures made in the Cedar River (2006) and the Indian and Hudson Rivers 

(2005–2006) when trout body temperatures were less than 20°C, cooler than the 

main stem by at least 1°C, cooler than the main stem by at least 2°C, cooler than 

the main stem by at least 1°C when river temperatures were greater than 20°C, 

and less than 20°C and also cooler than the main stem by at least 1°C when river 

temperatures were greater than 20°C ....................................................................................56

25. The relative importance (indicated with a predictor weight between 0 and 1, 

representing the likelihood that a parameter is the most important for explaining 

variability in temperature differences) of the three most important parameters for 

each river and time-block combination ..................................................................................61
xi

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C= (°F-32)/1.8

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Mesh sizes of sieves are given in micrometers (μm).

Coordinates for trout telemetry data are rcorded in Universal Transverse Mercator Zone 

(U18) coordinates.

List of Acronyms

CI Confidence intervals

EPT Ephemeroptera-Plecoptera-Trichoptera 

GCU Geomorphic channel units 

HBI Hilsenhoff’s Biotic Index 

MDS Multidimensional scaling 

NYSBAP New York State Biological Assessment Profile 

NYSDEC New York State Department of Environmental Conservation

PMA Percent model affinity 

RIT Rochester Institute of Technology 

TD Temperature differences 

USGS U.S. Geological Survey 

UWNY United Water New York

WSA Water Supply Application
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xiii

Executive Summary

The U.S. Geological Survey (USGS), New York State Department of Environmental Conservation 

(NYSDEC), and Cornell University completed a cooperative 2-year study from late 2004 to 2006 

to characterize the potential hydrologic, physical, and biological effects of the releases from 

Lake Abanakee on the Indian, Cedar, and Hudson Rivers in the Adirondack Mountains of New 

York. Researchers gathered baseline information on hydrology, temperature, habitat, wetlands, 

and communities of resident fish (brown trout) and macroinvertebrates. Collaborators with the 

Rochester Institute of Technology measured surface river-water temperatures in August 2005 

through remote (aerial) infrared imaging during base and high (release) flows.

This report summarizes important natural resources and evaluates differences in (1) selected 

physical (hydrology and temperature) conditions in a 17-mile-long1 reach of the Indian and 

Hudson Rivers downstream from the Abanakee Dam; (2) the frequency, duration, magnitude, 

and spatial extent of variations in hydrology and temperature related to the releases; 

(3) macroinvertebrate and fish communities, riparian wetlands, and instream-habitat data from 

most of the same sites (and from four control sites in the Cedar River); (4) the potential effects 

of flow releases on the biological resources of the Indian and Hudson Rivers; (5) the quality 

and quantity of thermal refuges in the three rivers under normal base flows and the effects of 

flow releases on thermal refuges in the Indian and Hudson Rivers; (6) the normal use of thermal 

refuges by brown trout during base flows in the three rivers and the potential effects of releases 

on trout behavior, survival, and use of thermal refuges in the Indian and Hudson Rivers; and 

(7) the level of drawdown (change in stage) in Lake Abanakee caused by the releases. 

The effects of the releases were assessed by comparing data from affected reaches with 

information from (1) the same reaches during nonrelease days, (2) control reaches in a nearby 

run-of-the-river system (the Cedar River), and (3) one reach in the Hudson River upstream from 

the confluence with the Indian River. 

River Discharge and Stage — Discharge for the Indian River at Lake Abanakee (site IR01) 

was usually higher in summer 2006 than in summer 2005; daily mean flows averaged 259 and 

443 cubic feet per second (ft3/s) during June, July, August, and September 2005 and 2006, 

respectively. The average base flow before releases in June, July, August, and September 

2006 was 349 ft3/s, which was nearly double the flow observed during the same period in 2005 

(180 ft3/s); however, the average peak discharges during releases in 2005 and 2006 (1,387 and 

1,410 ft3/s, respectively) were nearly equivalent. Discharge during the releases increased on 

average by 1,207 ft3/s and 1,061 ft3/s in the summer (June, July, August, and September) of 

2005 and 2006, respectively.

Mean increases in stage during releases in June, July, August, and September at the three 

Indian River sites ranged from 1.18 to 2.14 feet (ft) during 2005 and from 0.79 to 1.94 ft during 

2006. Mean monthly changes in stage during releases for study sites in the Hudson River ranged 

from 1.14 to 3.15 ft during 2005 and from 0.67 to 1.31 ft during 2006. Increases were smaller in 

2006 than in 2005 because base flows were generally higher during the summer of 2006. 

1 Unit conversions are shown in the conversion tables at the front of the report. 
xiv

In 2005, mean river stage and discharge during June, July, August, and September at IR01 

decreased by 0.23 to 0.27 ft (mean 0.25 ft) and 65 to 70 ft (mean 66 ft), respectively, below 

values prior to the release and after the gate was closed; river stage and flow did not fully 

rebound until the next release about 60 percent of the time. In 2006, mean river stage and 

discharge during June, July, August, and September at IR01 decreased by 0.13 to 0.33 ft 

(mean 0.23 ft) and 63 to 96 ft (mean 80 ft), respectively, below mean values prior to the release, 

after the gate was closed; river stage and flow did not fully rebound until the next release about 

46 percent of the time.

Lake Abanakee Stage — The releases caused the Lake Abanakee stage to consistently 

decrease by 0.30 ft on release days during June, July, August, and September of 2005 and 2006. 

Lake stage between releases fully rebounded to the stage before the release 50 percent of the 

time in 2005 and 58 percent of the time in 2006. The average recovery prior to the next release 

was 91 percent of the prerelease stage in 2005 and 98 percent of the prerelease stage in 2006. 

Lake levels dropped more than 0.30 ft only during gate malfunctions or when the gate was left 

open to alleviate risk of flooding around the shores of Lake Abanakee.

River Temperatures — The recreational flow releases appeared to cause no biologically 

relevant change in water temperatures at all study sites in the Indian and Hudson Rivers, even 

though mean and median temperatures on release days were significantly lower than mean 

and median temperatures on nonrelease days. Regardless of releases, water temperatures 

at all study sites commonly exceeded a threshold (20oC) known to be stressful to brown trout. 

The maximum water temperature for the period of record at Indian River below Lake Abanakee 

(IR01) was 26.5oC on July 18, August 9, and August 10, 2005. Water temperatures were higher 

at all sites in summer 2005 than in summer 2006; mean daily temperatures were 1.1, 1.6, and 

2.8oC greater in July, August, and September of 2005, respectively, than in the same months 

during 2006. The mean daily maximum temperatures at all study sites did not differ significantly 

on days with releases and days without releases. The releases caused no significant shortterm increase in river temperature at any study site, but they produced small (less than 0.5oC) 

significant decreases in water temperatures at three sites.

Stream Habitat — Short riffles dominated habitat at most Indian and Hudson River study sites 

during base flows, and fewer but larger habitat units were evident during the releases. Higher 

water velocities during releases increased the amount of fast-water habitat (rapid, riffle, run) 

and decreased the amount of slow-water habitat (pool, glide, backwater, side channel) at all 

study reaches. Habitat alterations were more pronounced in reaches nearer the dam; rapids 

were a dominant habitat unit in the Indian and upper Hudson reaches during release flows, but 

glides were a dominant habitat unit in the lower Hudson reaches during both release and base 

flows. Changes in water velocities and habitat during flow releases might force fish species to 

alter behaviors or be displaced from preferred habitat and (or) positions in the river.

Wetlands — Surveyed shorelines along the Indian River included fewer wetlands than control 

reaches in the Cedar River: wetlands composed 18 percent of the total length of Indian River 

shoreline, compared to 25 percent (upper reach) and 46 percent (lower reach) of the Cedar 

River shoreline. Although differences in wetland coverage between the two rivers may be 

partly related to the releases, the plausibility of both positive and negative effects of release 

flows on wetlands indicates that this issue is complicated. The Indian River may include 

fewer wetlands because of the decades-long presence of a major upstream dam. The flow 

releases scour fine sediments from the river bed and banks while the dam restricts the supply 
xv

of upstream sediment; both act to reduce the sustainability of wetlands. The current release 

schedule, however, may also help to maintain wetlands in the Indian River by allowing periodic 

inundation of perched wetlands in backwater areas. Further research is needed to support 

these hypotheses.

Remote Thermal Imaging Study — Data from the three thermal imaging flights, with the 

release bubble covering different sections of the 27-km study reach, showed that few thermal 

refuges (waters at least 1oC colder than the main channel) occurred in the study area under 

normal summer base flows. Five cold-water tributaries entering the Hudson River downstream 

from the Boreas River contained most of the potential thermal refuge areas in the study area. 

The high-flow bubble (peak stage moving through study reaches) produced by flow releases 

from Lake Abanakee eliminated most main-channel refuges. In the lower Indian River (km 4–5), 

a water-surface area of 1,606 m2 (4.24 percent) was at least 1oC colder than the main channel 

during base flows (third flight), but an area of only 56 m2 (0.15 percent) was at least 1oC colder 

during release flows (second flight). In the Hudson River Gorge (km 6-15), a water-surface area 

of 529 m2 (1.00 percent) was at least 1oC colder than the main channel during base flows (third 

flight), but an area of only 176 m2 (0.34 percent) was at least 1oC colder during release flows 

(second flight). In the lower Hudson River (km 20–27), a water-surface area of 515 m2 (0.68 

percent) was at least 1oC colder during base flows (second flight), but an area of only 22 m2

(0.03 percent) was at least 1oC colder than the main channel during release flows (third flight). 

Temperature data from the first flight were not included in this analysis because exposed 

rocks sometimes appeared to be thermal refuge; for instance, a surface area of 2,512 m2

(7.56 percent) in the Indian River (km 1–5) appeared to be at least 1oC colder than the main 

channel during release flows, but an area of only 220 m2 (1.25 percent) appeared to be at least 

1oC colder when only the unshaded half of the river was considered. Analysis of temperature 

patterns at different spatial scales show different effects of release water on quality of fish 

habitat. Water temperatures in the middle of the reach (Hudson River Gorge) were consistently 

cooler than in the upper and lower study reaches of the river, and the high-flow bubble did not 

diminish thermal refuges in this reach to the same extent as in upper and lower reaches.

Thermal imaging offers an effective way to identify and characterize cold-water refuges in 

streams with poor access; however, two issues diminish the utility of Indian River data and 

analyses. First, boundaries between water and land were not always discernible and had to be 

delineated manually because overhanging vegetation on color images hid some shorelines, and 

surface temperatures of the river and the rocky shorelines could not be separated electronically 

on digital images. Second, the analyses and results could be limited by these technical 

difficulties and by the general inability to detect seeps on the river bed.

Fish Assemblages — Fish-population and community data were collected and summarized 

through electrofishing surveys at 12 sites in the Cedar, Indian, and Hudson Rivers during 2005 or 

2006. Community indexes and density and biomass of individual fish populations were evaluated 

to test hypotheses that: (1) fish communities at all Indian River sites were negatively affected by 

the releases, and (2) fish communities at the four downstream sites on the Hudson River were 

moderately affected by the releases.

In the Indian River, fish communities appeared to be strongly affected by the releases at site 

IR01 and moderately affected at IR02 and IR03. Communities were slightly affected by the 

releases at the first study site in the Hudson River below the confluence with the Indian River 

(HR02) and either positively or not affected by releases at the remaining downstream Hudson 
xvi

River sites (HR04 and HR05). Significant differences between estimates of community biomass 

and density at IR01 and at the most upstream Cedar River site (CR01) and the slight decrease 

in both estimates at HR02 indicate that fish communities at IR01 and HR02 were atypical. 

Community richness was consistently one to six species lower at the three Indian River sites 

than at all other study sites and three to six species lower than at the two downstream sites 

on the Cedar River. Community diversity, equitability, and dominance did not differ significantly 

among study sites in the three rivers. Significant differences in average community richness 

values at the three Indian River sites and at study sites in the Hudson River and in the Cedar 

River (aggregated by river) indicate that the releases may adversely affect the number of fish 

species in the Indian River. Species richness, diversity, and equitability were generally higher, 

and dominance at the three Hudson River sites downstream from the confluence with the Indian 

River (HR02, HR04, and HR05) was lower than at HR01, indicating that community function at 

the three affected Hudson River sites was altered slightly. Community structure at these three 

sites, however, was more balanced than the community at the control site HR01. The decreasing 

indexes with increasing drainage were opposite those observed in the Indian River and indicate 

either that natural variability in community indexes was high and the effects could not be 

quantified, or that the fishery was negatively affected when relative changes in flow were large 

and positively affected when relative changes in flow were moderate.

The changes in the density and biomass of individual fish populations as a result of flow 

releases were generally similar to changes in the community indexes. The releases had a 

strong effect on the densities of individual fish populations at the three Indian River study 

sites, whereas the effects of the releases on fish populations in the Hudson River were either 

less obvious, nonexistent, or contrary to what was expected. The releases appeared to reduce 

the number of fish species and slightly decrease the abundance of some endemic species in 

the Indian River. Flow releases may have also caused small changes in the densities of some 

species at several Hudson River sites, replacement of a few species at HR02 and HR04 (rather 

than species losses as noted for the Indian River), and little or no adverse effects at HR05. The 

total biomass of dominant species populations was severely affected by the releases only at 

IR01. The total biomass of species populations at Hudson River study sites reflected the addition 

of several species and small decreases or no change in species abundance. The balance of 

species populations generally increased as indicated by increases in community equitability at 

sites farther downstream; these trends appeared to be unrelated to the releases.

Biomass can be a better gauge of community disturbance than density because measures of 

biomass tend to fluctuate less widely than density when communities are affected by biotic, 

habitat, and water-quality stresses. Biomass data for species populations in this study were less 

variable (total biomass varied by a factor of 6) among sites than density (total density varied by 

a factor of 94). The biomasses of cutlips minnow, longnose dace, smallmouth bass, and rock 

bass populations at CR04, IR02, IR03, and possibly HR01 were relatively well balanced and 

similar to each other, but they generally differed from biomasses of species populations at sites 

farther upstream in the Cedar River. Biomasses of species populations at Indian River sites IR02 

and IR03 were generally comparable to those observed at the two control sites, CR04 and HR01. 

Differences between the total biomass of populations at Indian River sites IR02 and IR03 and 

at the Cedar River sites CR01 and CR02 may be related to low densities of predator species at 

upstream Cedar River sites (above the Cedar Dam) or to different environmental conditions at 

the lower Indian River sites. The total community biomass at potentially affected Hudson River 

sites (HR02–HR05) was dominated by three to six species, including common shiner, fallfish, 

white sucker, cutlips minnow, smallmouth bass, and trout, whereas the total biomass at the 
xvii

control site (HR01) was dominated by smallmouth bass, rock bass, cutlips minnow, and central 

mudminnow. Except for sites HR01 and HR02, the biomass of fish populations was relatively 

well balanced in communities at most Hudson River study sites.

Other unmeasured factors may have also contributed to, or caused the observed differences in, 

population and community indexes among study sites in the three rivers. Additional replicated 

fish-community data, hydrologic data, and more detailed habitat information would be needed 

to fully document site-to-site similarities and differences and evaluate whether differences 

in population and community indexes were caused mainly by releases or by a combination of 

physical, chemical, and biological factors.

Macroinvertebrate Communities — Macroinvertebrate community data were summarized 

for surveys done at 12 study sites in the Cedar, Indian, and Hudson Rivers during 2005 and 2006; 

however, only results from 2006 were assessed to test hypotheses that macroinvertebrate 

communities at all Indian River sites were negatively affected by the releases, and that 

macroinvertebrate communities at the four downstream sites on the Hudson River were 

moderately affected by the releases.

Separate analyses of macroinvertebrate community indexes, functional feeding guilds, dominant 

species, and Bray-Curtis similarities provided complementary findings. Estimates of community 

richness were at or below the slightly affected (lower) threshold of 26 species only at CR01 and 

the three Indian River sites during 2005 and at two additional Cedar River and three Hudson 

River sites during 2006. The New York State Bioassessment Profile (NYSBAP) scores were 

below 7.5 only at CR01 and IR01 during 2005 and at all three Indian River sites and CR01 and 

CR04 during 2006. The factors that affect invertebrate communities in the Cedar and Indian 

Rivers appear to be analogous because NYSBAP scores (and most other metrics) were not 

significantly different between the sites immediately downstream from the dams in both rivers 

(IR01 and CR01). Analyses of feeding guilds and differences in dominant macroinvertebrate taxa 

generally confirm impoundment effects and indicate that macroinvertebrate communities at 

the study sites were similar during 2005 and 2006. The 2006 data indicate that sites affected 

by impoundments (IR01, IR02, and CR01) generally had much lower percentages of collector 

gathers and scrapers and much higher percentages of filterers than most unaffected sites farther 

downstream from impoundments. No major differences were noted between the percentages 

of feeding guilds at HR01 and four other Hudson River sites. The composition of feeding guilds 

at CR01 and IR01, as well as those at IR02 and IR03, provide strong evidence for impoundment 

effects on food webs at riverine sites immediately downstream from both dams. A cluster 

analysis of Bray-Curtis similarities identified no unique effects in the Indian River caused by 

flow releases, but showed strong and similar impoundment effects at the two sites immediately 

downstream from the dams (IR01 and CR01), an undefined effect at CR04, diminishing effects at 

sites farther downstream in the Indian River (2 to 4 km below the dam), minor or no effects at 

downstream Cedar River sites (8 to 54 km below the dam), and no distinguishable effects at all 

Hudson River sites.

Overall, the results indicate that function and integrity (health) of macroinvertebrate 

communities at all Indian, Cedar, and Hudson Rivers were generally not affected by water 

quality, which ranged from very good to good. The strong effects on macroinvertebrate 

communities at sites immediately downstream from both dams could be attributed primarily to 

the comparable quality of waters discharged from respective impoundments. The near absence 

of scrapers at all Indian River sites and the presence of two unique species (blackflies and pea 
xviii

clams) at IR01 indicated there were some minor effects on benthic invertebrate assemblages 

by the releases. The lack of significantly different mean NYSBAP scores and other indexes 

between HR01 and the four other Hudson River sites downstream from its confluence with the 

Indian River during 2005 and 2006, and the fact that all Hudson River sites were classified as 

unaffected during both 2005 and 2006, indicates that the releases (and the impoundment) had 

few or no adverse effects on benthic macroinvertebrate communities in the Hudson River.

Trout Behavior — The use of thermal refuges by stocked brown trout varied among study 

reaches and ranged from low to moderate levels in the three rivers. Telemetry observations 

indicated that brown trout used thermal refuges to maintain body temperatures at least 1oC 

cooler than the main-stem river (trout-body temperature differences (TDs) were at least 1oC 

cooler than the river) 29 percent of the time in the Hudson River, 38 percent of the time in 

the Cedar River, and about 4 percent of the time in the Indian River. Observations when river 

temperatures were warmer than 20oC and TDs were at least 1oC cooler than river waters 

indicate that brown trout used thermal refuges 33 percent of the time in the Hudson River, 

30 percent of the time in the Cedar River, and 4 percent of the time in the Indian River. 

Observations when river temperatures were warmer than 20oC, trout temperatures were less 

than 20oC, and TDs were at least 1oC cooler than the river indicate that brown trout used 

thermal refuges 9 percent of the time in the Hudson River, 17 percent of the time in the Cedar 

River, and 1 percent of the time in the Indian River.

The releases generally decreased the ability of many trout to benefit from thermal refuges in 

the Indian and Hudson Rivers. Multilevel-effect analyses indicated that the releases had a 

significant negative effect on thermoregulation of trout in the Indian River and on trout within 

50 m of a tributary in the Hudson River. When ambient river temperatures were thermally 

stressful, releases increased average temperatures of brown trout by less than 0.5oC in the 

Indian River and by more than 1.0oC in the Hudson River; however, the biological significance 

of this reduced ability to thermoregulate remains uncertain for several reasons. First, very few 

trout used thermal refuges in the Indian River. Brown trout near tributaries in the Hudson River 

occasionally maintained cooler temperatures or moved into cooler waters during releases. 

A limited number of observations before and during releases (span data) show that body 

temperatures did not change (80 percent) or increased (20 percent) in the Indian River and did 

not change (41 percent), increased (38 percent), or decreased (22 percent) in the Hudson River 

during releases. The releases, however, may have only a small effect on individual brown trout 

(and their populations) in the Indian and Hudson Rivers because few thermal refuges exist 

in both reaches, and relatively few study trout were found to exploit them. Although some 

naturalized brown trout may be present in the system, we assume that the behavior of telemetry 

(study) brown trout was comparable to the behavior of most resident brown trout because both 

groups originated from local hatcheries as 2-year olds and few generally overwintered.

Rates of trout movement and apparent survival during the telemetry study differed among study 

reaches and illustrate the different effects of unique thermal refuges and flow regimes on brown 

trout in the three river systems. The daily movement of trout was greater in study reaches 

in the Hudson River than in either the Indian or Cedar Rivers, and movement was generally 

unaffected by releases in the Indian and Hudson Rivers. In all study reaches, some trout 

dispersed from stocking locations within 24 to 48 hours. Over time, most trout tended to inhabit 

a few specific locations, usually in deep pools or runs or near tributary confluences. Different 

trout activity levels among the three study reaches may be related to variations in stream 

gradient and general habitat conditions. The apparent survival time for stocked trout was very 
xix

low and similar in the Indian and Hudson Rivers during 2005 and 2006 but significantly higher 

in the Cedar River than in the other rivers during 2006. Fewer than 12 percent of trout stocked 

into affected reaches in the Indian and Hudson Rivers survived through both years, whereas 

53 percent of trout in the Cedar River survived during 2006. More than 20 percent of dead trout 

and transmitters were found or inferred to be in the forest, sometimes in burrows or a rookery, 

indicating that predation was an important source of mortality. Other causes of mortality were 

likely angling, thermal stress, and starvation caused by the high metabolism rate required 

for survival.
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Effects of Recreational Flow Releases on Natural 

Resources of the Indian and Hudson Rivers in the Central 

Adirondack Mountains, New York, 2004–06

By B.P. Baldigo, C.I. Mulvihill, A.G. Ernst, and B.A. Boisvert1

using standard indices. Radio telemetry was used to track the 

movement and persistence of stocked brown trout (implanted 

with temperature-sensitive transmitters) in the Indian and 

Hudson Rivers during the summer of 2005 and in all three 

rivers during the summer of 2006.

The releases had little effect on river temperatures, 

but increased discharges by about one order of magnitude. 

Regardless of the releases, river temperatures at all study 

sites commonly exceeded the threshold known to be stressful 

to brown trout. At most sites, mean and median water 

temperatures on release days were not significantly different, 

or slightly lower, than water temperatures on nonrelease days. 

Most differences were very small and, thus, were probably 

not biologically meaningful. The releases generally increased 

the total surface area of fast-water habitat (rapids, runs, and 

riffles) and decreased the total surface area of slow-water 

habitat (pools, glides, backwater areas, and side channels). 

The total surface areas of wetlands bordering the Indian River 

were substantially smaller than the surface areas bordering 

the Cedar River; however, no channel geomorphology 

or watershed soil and topographic data were assessed to 

determine whether the releases or other factors were mainly 

responsible for observed differences.

Results from surveys of resident biota indicate that 

the releases generally had a limited effect on fish and 

macroinvertebrate communities in the Indian River and had 

no effect on communities in the Hudson River. Compared to 

fish data from Cedar River control sites, the impoundment 

appeared to reduce total density, biomass, and richness in 

the Indian River at the first site downstream from Lake 

Abanakee, moderately reduce the indexes at the other two 

sites on the Indian River, and slightly reduce the indexes at 

the first Hudson River site downstream from the confluence 

with the Indian River. The densities of individual fish 

populations at all Indian River sites were also reduced, but 

related effects on fish populations in the Hudson River were 

less evident. Although statistical comparisons (and defensible 

conclusions) were not possible with the limited fishery data, 

the findings suggest that both the releases and the unique 

habitat (physical, chemical, and thermal features) of the lower 

Abstract

The U.S. Geological Survey (USGS), the New York 

State Department of Environmental Conservation (NYSDEC), 

and Cornell University carried out a cooperative 2-year 

study from the fall of 2004 through the fall of 2006 to 

characterize the potential effects of recreational-flow releases 

from Lake Abanakee on natural resources in the Indian and 

Hudson Rivers. Researchers gathered baseline information 

on hydrology, temperature, habitat, nearshore wetlands, and 

macroinvertebrate and fish communities and assessed the 

behavior and thermoregulation of stocked brown trout in 

study reaches from both rivers and from a control river. The 

effects of recreational-flow releases (releases) were assessed 

by comparing data from affected reaches with data from the 

same reaches during nonrelease days, control reaches in a 

nearby run-of-the-river system (the Cedar River), and one 

reach in the Hudson River upstream from the confluence with 

the Indian River.

A streamgage downstream from Lake Abanakee 

transmitted data by satellite from November 2004 to 

November 2006; these data were used as the basis for 

developing a rating curve that was used to estimate discharges 

for the study period. River habitat at most study reaches was 

delineated by using Global Positioning System and ArcMap 

software on a handheld computer, and wetlands were mapped 

by ground-based measurements of length, width, and areal 

density. River temperature in the Indian and Hudson Rivers 

was monitored continuously at eight sites during June through 

September of 2005 and 2006; temperature was mapped in 

2005 by remote imaging made possible through collaboration 

with the Rochester Institute of Technology. Fish communities 

at all study reaches were surveyed and characterized 

through quantitative, nearshore electrofishing surveys. 

Macroinvertebrate communities in all study reaches were 

sampled using the traveling-kick method and characterized 

1

Cornell University, USGS-NY Cooperative Fish & Wildlife Research 

Unit, 208 Fernow Hall, Ithaca, NY 14853-3001; Nov. 2010: AKRF, Inc., 307 

Fellowship Road, Suite 214, Mt. Laurel , NJ 08054
2 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

Indian River are responsible, at least in part, for the character 

of the local fish populations and communities. The effects of 

both impoundments on macroinvertebrate communities in 

the Indian and Cedar Rivers were prominent and appear to 

overwhelm or mask possible effects related to the recreational 

releases. Compared to macroinvertebrate data from Cedar 

River control sites, the releases had small significant effects 

on macroinvertebrate assemblages and dominant species in the 

Indian River, and they occurred primarily downstream from 

the Lake Abanakee Dam. The macroinvertebrate communities 

at the Hudson River control site did not differ significantly 

from those at all other Hudson River sites and indicates that 

the effects of the impoundment and the releases did not extend 

much beyond its confluence with the Indian River.

The thermal-imaging and fish-telemetry results confirm 

that river temperatures in the Indian and Hudson study reaches 

were usually stressful to brown trout during the warm summer 

months. Few thermal refuges (defined as water at least 1°C 

cooler than the temperature in the main channel) were evident 

in both rivers during normal summer base flows, and use of 

these refuges by brown trout was typically low to moderate 

during 2005 and 2006. A few cold-water tributaries to the 

Hudson River provided limited areas of thermal refuges, but 

the releases from Lake Abanakee effectively eliminated these 

refuges by swamping them with warmer water. Multileveleffect analyses indicate that the releases significantly reduced 

the ability of trout to thermoregulate themselves in the Indian 

and Hudson Rivers. The releases should ostensibly have only 

negligible effects on brown trout in the Indian and Hudson 

Rivers because few thermal refuges exist in both reaches, and 

relatively few study trout were found to exploit them. Trout 

movement was unaffected by the flow releases, but persistence 

of trout was low in the Indian and Hudson Rivers during 2005 

and 2006 and higher in the Cedar River during 2006. 

Introduction

The Hudson Gorge Primitive Area and the lower Indian 

River in the Adirondack Mountains of northeastern New 

York support small transient populations of native brook trout 

(Salvelinus fontinalis) and seasonal populations of hatchery 

(stocked) brown trout (Salmo trutta) and rainbow trout 

(Oncorhynchus mykiss). The river’s extensive whitewater 

reaches also provide a setting for a commercial rafting 

industry that operates from April through October. The Town 

of Indian Lake owns and operates a raft-launching site on 

the Indian River about 5 km1 above its confluence with the 

Hudson River and just downstream from the Lake Abanakee 

Dam. The town makes top-water releases from the dam 4 days 

1

Unit conversions are shown in the conversion tables at the front of the 

report.

each week during the spring, summer, and fall to increase river 

stages along a 17-mi reach of the Indian and Hudson Rivers. 

These 1.5-to-2 hour releases are vital to the rafting industry 

because they augment river stages and permit rafting during 

summer months when flows would normally be too low for 

rafters to easily navigate the river. Local anglers, however, 

are concerned that the releases decrease abundance of wild 

and stocked trout by directly or indirectly decreasing their 

growth, survival, or both. Anglers assume that high flows 

caused by the recreational flow releases (termed releases 

from here on) potentially increase thermal stresses, physically 

injure or kill trout, force trout to flee the area, decrease the 

quantity or quality of prey that trout prefer (minnow or benthic 

macroinvertebrate species), or potentially decrease the quality 

and quantity of suitable fish habitat or thermal refuges

Water temperature is a critical component of fish habitat 

in the lower Indian and the upper Hudson Rivers because 

it ranges near or above thresholds for survival of brook 

trout (24°C), brown trout (25°C), and rainbow trout (27°C) 

(Raleigh, 1982; Raleigh and others, 1984; Raleigh and 

others, 1986) for extended periods during summer months 

(Richard Preall, New York State Department of Environmental 

Conservation, written commun., 2003). Releases from Lake 

Abanakee during the warmest months of the year augment 

flows in downstream riverine reaches when water temperatures 

in both rivers, as well as in Lake Abanakee, are sometimes at 

or above thresholds lethal to salmonids and when combined 

inputs (volume) from cold-water tributaries and groundwater 

seeps along shorelines in both rivers are minimal. It is well 

known that trout often move to areas of their preferred 

temperatures to maximize growth, fitness, and survival (Power 

and others, 1999; Torgersen and others, 1999; Ebersole and 

others, 2003). Several studies found that salmonids actively or 

passively relocate to cool-water refuges, if present, to avoid 

lethal stresses as water temperatures approach the limits they 

can tolerate (Bermann and Quinn, 1991; Power, 1997; Baird 

and Krueger, 2003). Summer releases of water from Lake 

Abanakee may decrease the quality and number of cool-water 

habitats (thermal refuges) available to trout by overwhelming 

these areas, which are typically small, with high volumes of 

release water. No one, however, knows (1) how many areas of 

cooler water (thermal refuges) are in sections of both rivers, 

(2) whether the quality, numbers, or volumes of potential 

thermal refuges change during releases, (3) whether trout 

stocked into the lower Indian and upper Hudson Rivers in 

spring use thermal refuges during summer, and (4) whether 

trout can avoid thermal stresses during summer by finding and 

occupying thermal refuges during normal (base) flows as well 

as during higher release flows.

High velocities of river water during releases may 

injure and weaken trout or physically displace them farther 

downstream, subsequently eradicating them from stocked 

locations. Trout (and other fish species) may also become 

stranded, only to expire on shorelines after dam gates are 
Measuring the Effects of Recreational Flow Releases on Habitat and Biological Communities 3

closed and as elevated flows (or stage) recede throughout 

the system. Stocked trout that occupy shallow shoreline 

areas during flow releases may also be more susceptible to 

predation. Releases may also affect other fish species that trout 

prey upon, thereby disturbing the entire fish community in 

parts of each river. Aside from direct effects on fish species, 

the hydrologic properties of flow releases may also cause 

shifts in assemblages of macroinvertebrate species and may 

modify benthic communities that some fish species use as a 

primary food source. These factors, alone or in combination, 

could disrupt aquatic ecosystems, substantially alter normal 

fish communities, and yield lower numbers and biomass of 

fish in reaches throughout both rivers. Any disruptive effects 

of releases would be more obvious at upstream sites and less 

severe farther downstream because supplementary flows from 

existing sources attenuate hydrologic variations that releases 

may cause.

The U.S. Geological Survey (USGS), the New York 

State Department of Environmental Conservation (NYSDEC), 

and Cornell University began a cooperative 2-year study in 

late 2004 to generate baseline information on the behavior 

of stocked trout, hydrology, temperature, habitat, wetlands, 

resident fish, and macroinvertebrate communities in the Indian 

and the Hudson Rivers. The Rochester Institute of Technology 

(RIT) added a study component on the remote imaging of 

surface-water temperatures in 2005. Primary objectives of this 

study were to document and evaluate the potential effects of 

the releases on natural resources and on the survival of stocked 

trout within affected reaches of both rivers. 

This report summarizes the baseline physical and 

biologic conditions at seven fixed sites downstream from Lake 

Abanakee in the Indian and the Hudson Rivers, variations in 

selected hydrologic and thermal regimes at these sites due to 

flow releases, temperature and biology data from four control 

sites in the Cedar River and one control site in the Hudson 

River, changes in surface-water elevation (lake stage) in Lake 

Abanakee due to releases, the quantity and quality of thermal 

refuges in the Indian and Hudson Rivers under normal and 

release flows, and the use of thermal refuges by trout under 

normal and release flows during 2004–06.

Effects of flow releases on fish and macroinvertebrate 

resources were qualified or quantified by comparing data from 

affected reaches with data from control reaches (physically 

similar, but unaffected by the releases) at nearby control sites 

in the Cedar River, a run-of-the-river system or at one reach 

in the Hudson River upstream from its confluence with the 

Indian River. Differences in trout behavior, survival, and body 

temperatures on release and nonrelease days between study 

reaches on the Indian and Hudson Rivers and control reaches 

on the Cedar River were used to assess potential effects of 

releases on the availability and use of thermal refuges by trout 

in the three rivers.

Measuring the Effects of Recreational 

Flow Releases on Habitat and 

Biological Communities

Point sampling and reach-wide assessments were used 

to characterize habitat, wetlands, temperatures, and trout 

behavior and evaluate the effects that releases from Lake 

Abanakee have on natural resources in the Indian and the 

Hudson Rivers. Detailed information on study reaches and 

sampling and analytical methods are provided below. 

Study Sites

Fourteen sites were selected for study: two on Lake 

Abanakee, three on the Indian River, five on the Hudson 

River, and four on the Cedar River (fig. 1, table 1). Unlike 

the waters from Lake Abanakee, waters from Wakely Dam 

(fig. 1) flow freely into the Cedar River, thereby providing 

a run-of-the-river flow regime. Extensive sampling efforts 

in the Cedar River were not part of the initial study design; 

however, comparable biology and limited temperature data 

were collected from four sites in the system using identical 

sampling methods (fig. 1 and table 1).

Stage, Discharge, and Water Temperature

A USGS streamgage was constructed on the Indian 

River just downstream from Lake Abanakee (IR01, fig. 1). 

Discharge at this site was estimated from the stage-todischarge relation, or rating curve, that was generated from 

periodic flow measurements made by USGS personnel. 

Pressure transducers were installed at two sites on Lake 

Abanakee (AB01 and AB02, fig. 1), two additional sites on 

the Indian River (IR02 and IR03, fig. 1), and five sites on 

the Hudson River (HR01–HR05, fig. 1). Dataloggers at all 

sites were programmed to measure stage and temperature at 

15-minute intervals. Streamgage 01315081 (IR01) transmitted 

near-real-time data on stage and water temperature by satellite 

from November 2004 to November 2006. Daily data on stage, 

discharge, and water temperature for this gage are available at 

http://nwis.waterdata.usgs.gov/.

Pressure transducers, which were used to collect stage 

and water-temperature data at nine sites, were housed in 

weather-resistant cylindrical enclosures attached to a 25-ft 

cable with a sensor at its end. At each site, the sensor, cable, 

and transducer were placed inside a 2-in.-diameter steel pipe, 

which was securely anchored to trees, bridge abutments, 

or boulders. Investigators used a handheld computer to 

periodically download data..

Records— Stage and water-temperature data were 

collected at 15-minute intervals at all sites (table 2). 
4 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

Equipment or battery failures led to gaps in continuous 

records at some sites. Missing temperature records at several 

sites were approximated from temperature data at the closest 

upstream site by using the average lag time between release 

stages and temperatures and the relation between water 

temperatures at both sites.

Data Analysis —The following procedures were used 

to analyze all stage and water-temperature data collected 

from the months of June to September in 2005 and in 2006 

to determine whether stage and water temperature changed 

significantly during releases from Lake Abanakee. 

• Water temperature and stage at the start and peak of 

each release were identified and used to calculate the 

total change in each of these variables at each site 

during release days. 

• The same calculation was made on nonrelease days for 

the time interval between start and peak on the prior 

release day.

• The monthly mean change of each variable was 

calculated for release days and for nonrelease days.

• A t-test was used to determine whether mean 

changes in stage or temperature on release days 

differed significantly from mean changes in stage or 

temperature on nonrelease days

Stream Habitat

River-habitat features, in the form of geomorphic 

channel units (GCUs), were measured along the Indian River 

study section during August and September 2005 (fig. 2) 

and along four reaches of the Hudson River study section 

during August 2007. Seven GCUs were identified: riffle 

(turbulent white water), rapid (faster than a riffle, with greater 

changes in gradient), run (laminar flow that is faster along 

well defined thalweg), pool (deep, slow water along thalweg), 

glide (laminar flow with uniform channel depth), backwater 

(slow-velocity, protected water separated from main channel), 

28N

74°24' 74°12' 74°

43°48'

43°42'

28

28

30

Deer C reek

Raquet te Brook

Aldous Broo k

Thirteenth Brook

Ba ml ofGilead

Brook

Brook

Griffin

Base from U.S. Geological Survey Digital Data.

Universal Transverse Mercator Projection, Zone 18N, NAD83

WARREN COUNTY

Wakely

Dam

EXPLANATION

Village and name

Study site

and identifier

Indian Lake

North River

0 3 6 KILOMETERS

0 3 6 MILES

Indian Lake

Cedar River

Dam

Boreas River

Indian River

Hudson River

Indian Lake

HAMILTON COUNTY

ESSEX COUNTY

Cedar River 

Flow

Thirteenth Lake

Lake Abanakee

Cedar River

Hudson River

Abanakee

Dam

Browns Brook

Brook

B ear

Trap

Map Area

NEW YORK

Adirondack

Park

78° 76° 74°

42°

44°

Warrensburg

CR04

CR03

CR02

CR01

HR05

HR04

HR03

HR02

HR01

IR03

IR02

IR01

AB02

AB01

CR01

Figure 1. Map showing lLocations of study sites and dams on the Indian, Hudson, and Cedar Rivers, Adirondack 

Mountains, New York. Study-site codes are listed in table 1.
Measuring the Effects of Recreational Flow Releases on Habitat and Biological Communities 5

Table 1. Characteristics of 14 study sites at Lake Abanakee and on the Indian, Hudson, and Cedar Rivers in the Adirondack Mountains, New York, 2005 and 2006.[Site locations are shown in figure 1; unit conversions are shown in the conversion tables at the front of the report. Latitude and longitude are in degrees, minutes, and seconds; km2, square kilometers; USGS, U.S. Geological Survey]

Site code Site name Latitude Longitude

Drainage area, 

square 

kilometers

USGS 

streamgage

number

Characteristics observed or measured

Lake Abanakee

AB01 Lake Abanakee near Indian Lake 43 45 40.5 74 15 04.6 476 01315064 water temperature, stageAB02 Lake Abanakee at Route 28 bridge near Indian Lake 43 47 05.1 74 14 22.8 487 01315072 water temperature, stage

Indian River

IR01 Indian River below Abanakee Dam near Indian Lake 43 47 55.4 74 13 46.3 505 01315081 water temperature, stage, discharge, 

fish communities, macroinvertebrate communities

IR02 Indian River above mouth near Indian Lake 43 48 47.6 74 12 37.5 513 01315083 water temperature, stage, fish communities, 

macroinvertebrate communities

IR03 Indian River at mouth near Indian Lake 43 49 21.4 74 11 40.0 518 0131508505 water temperature, stage, fish communities, 

macroinvertebrate communities

Hudson River

HR01 Hudson River at Gooley near Indian Lake 43 50 03.0 74 11 45.1 1,085 01314000 water temperature, stage, fish communities, 

macroinvertebrate communities

HR02 Hudson River below Indian River near Indian Lake 43 49 25.8 74 11 31.8 1,626 0131508508 water temperature, stage, fish communities, 

macroinvertebrate communities

HR03 Hudson River near North River 43 49 10.0 74 08 18.1 1,655 01315095 water temperature, stage, 

macroinvertebrate communities

HR04 Hudson River above Boreas River near North River 43 47 50.6 74 03 00.1 1,691 0131511503 water temperature, stage, fish communities, 

macroinvertebrate communities

HR05 Hudson River at North River 43 44 40.5 74 03 30.8 1,968 01315340 water temperature, stage, fish communities, 

macroinvertebrate communities

Cedar River

CR01 Cedar River below Wakely Dam near Indian Lake 43 43 38.9 74 28 18.5 117 01312710 fish communities, 

macroinvertebrate communities

CR02 Cedar River above Brown’s Brook near Indian Lake 43 46 46.0 74 25 25.0 149 01312790 fish communities, 

macroinvertebrate communities

CR03 Cedar River above Bear Trap Brook near Indian Lake 43 46 59.0 74 19 55.0 213 01312925 fish communities, 

macroinvertebrate communities

CR04 Cedar River above mouth near Indian Lake 43 51 21.0 74 13 22.0 425 01313600 fish communities, 

macroinvertebrate communities
6 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06 Table 2. Dates when data on river stage and temperature were collected at 10 study sites on Lake Abanakee and the Indian and Hudson Rivers in 2005 and 2006. [Stage and discharge data for IR01, and temperature data for all other sites are available at http://nwis.waterdata.usgs.gov/. Locations of study sites are shown in figure 1; site codes are listed in table 1; na, no data available] Site 2005 2006 River stage River temperature River stage River temperature AB01 6/25–7/23, 8/19–9/6 6/25–10/27 na na AB02 7/1–8/9, 8/20–9/29 6/30–10/27 3/30–9/28 3/30–9/28 IR011 1/1–12/31 1/1–12/31 1/1–11/30 1/1–11/30 IR02 6/25–9/30 6/25–10/27 5/16–9/28 5/16–9/28 IR03 7/1–9/30 6/30–10/27 5/24–9/26 5/24–9/26 HR01 7/1–9/30 8/4–9/20 5/24–9/21 2/16–9/20 HR02 7/1–8/7, 8/30–9/30 6/30–8/25, 9/20–10/5 4/20–6/21 4/20–6/21 HR03 6/28–8/8, 8/20–9/30 6/28–11/14 4/20–5/26, 6/13–6/26 4/20–5/26, 6/13–6/26 HR04 6/28–9/30 6/28–10/27 4/20–9/26 4/20–9/26 HR05 6/25–8/13, 8/20–9/30 6/25–10/27 3/30–6/28 3/30–6/28, 8/14–9/26 1 Discharge data are available only for this site in 2005 and 2006. 
Measuring the Effects of Recreational Flow Releases on Habitat and Biological Communities 7

Rapid

Rapid

Run

Run

Run

Riffle

S Riffle ide

channel

EXPLANATION

Study site

Geomorphic channel units in sampled area

 measured during high flow 

IR01

IR02

IR03

Abanakee Dam

Indian River

Hudson River

0.3 MILE

0 0.3 KILOMETER

0

0.8 MILE

0 0.8 KILOMETER

0

Base from New York State Office of Cyber Security, 1994−1999,

One Meter Color Infrared Orthoimagery,

Universal Transverse Mercator, Zone 18, NAD 83

Figure 2. Aerial photograph of the Indian River from Abanakee Dam (lower left corner) to downstream confluence 

with the Hudson River (upper right corner), Adirondack Mountains, New York. Inset shows details of the sampled 

area, including labeled geomorphic channel units. Locations of the study sites are shown in figure 1; study-site 

codes are listed in table 1.
8 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

and side channel (channel that diverges from the main stem, 

then rejoins it). Indian River GCUs were mapped during 

base flow over the entire study segment and again at high 

flow over two shorter reaches that included three stage-depth 

dataloggers in the river segment (figs.1, 2). Hudson River 

GCUs were mapped during base flow and high flow along 

400- to 1000-m reaches near each of the four stage-depth 

dataloggers (HR02–HR05). Each GCU was digitally traced 

into a handheld computer by using a global positioning system 

(GPS) and ArcMap 6.0 software. Water depth, velocity, and 

substrate size were measured at three points across a randomly 

selected transect within each GCU during base flow only.

Distribution of Wetlands

Wetlands were mapped along both banks of the entire 

Indian River during base flow in August and September 

2005 and along one bank of two reaches of the Cedar River 

in September 2006 (fig. 3). Wetlands were identified by 

vegetation types and accumulations of soils. The area of each 

wetland was calculated by multiplying its length (along the 

edge of the river) by the average of three measurements of its 

width and by the areal density of the wetland patch. Area was 

not calculated for wetlands in the upper Cedar River reach 

because many of its wetlands lay on the narrow sides of steep 

Figure 3. Map showing wWetlands on sections of the Indian and Cedar Rivers, Adirondack Mountains, New York. 

Locations of study sites are shown in figure 1. Grey color denotes areas where no data were collected.

EXPLANATION

Wetland location on the upper Cedar River 

Wetland location on the lower Cedar River 

Wetland location on the Indian River

Cedar River

Indian River

Base from New York State Office of Cyber Security, 1994−1999,

One Meter Color Infrared Orthoimagery,

Universal Transverse Mercator, Zone 18, NAD 83
Measuring the Effects of Recreational Flow Releases on Habitat and Biological Communities 9

banks. Only wetlands of area greater than 200 ft2 or patchy 

wetlands that covered 200 ft2 in a 600-ft2 area were counted; 

however, all wetlands in the upper Cedar River were included 

(fig. 3).

Temporal and Spatial Patterns in 

River Temperature

Scientists from the Chester F. Carlson Center for Imaging 

Science at the Rochester Institute of Technology used airborne 

thermal remote sensing to map surface-water temperatures 

along the Indian and the Hudson Rivers downstream from 

Lake Abanakee to North Creek, NY. Sensors collected shortwave, medium-wave, and long-wave infrared and visiblespectrum data during three low-altitude flights in an airplane 

equipped with visible-light (red-green-blue band) and forwardlooking infrared cameras. Digital temperature data were 

calibrated against data from the seven instream dataloggers, 

providing a resolution of less than 1oC. Thermal imagery data 

were collected on August 25, 2005, a release day, during three 

flights that recorded data at most points along both rivers 

during low and high flows (before, during, and after a release). 

No single flight captured images of the entire reaches in 

both rivers during either low or high flow. IMAGINE imageprocessing software (ERDAS, 1995) and ArcGIS (ESRI, 

1995) were used to process and analyze thermal imagery data.

Objectives of the thermal imagery surveys were to 

(1) document overall temperature patterns in the Indian and 

Hudson Rivers under base and release flows, (2) quantify 

the area and quality of thermal refuge available to resident 

trout during base flow, and (3) evaluate changes in thermal 

refuges in both rivers that were associated with the releases. 

Each of the three flights collected data from a different section 

of the 27-km reach during high flows. For this reason, data 

were processed along the whole river and in 1-km sections, 

in longitudinally split 0.5-km sections, and at cold-water 

tributary confluences to enable researchers to evaluate each 

section separately at low and at high flows. In addition, a 

longitudinal temperature profile along the whole river for 

each flight was generated by the investigators. A separate 

manuscript (Ernst and others, in press) provides further details 

outlining the collection and analysis of thermal-imagery data

Fish Communities 

Near-bank fish communities along river margins at 

seven sites on the Indian and Hudson Rivers (IR01, IR02, 

IR03, HR01, HR02, HR04, and HR05; fig.1) and one site 

on the Cedar River below Wakely Dam (CR01; fig. 1) were 

characterized during July and August 2005 by electrofishing 

methods. Fish communities were surveyed at three additional 

sites on the Cedar River: above Browns Brook (CR02), above 

Bear Trap Brook (CR03), and above the mouth of the Cedar 

River (CR04) during August 2006 (fig. 1). Fish communities 

at HR03 were not surveyed because the site was too 

remote. At each study site, two or three near-bank locations 

(subreaches) were blocked off with a longitudinal 80-ft seine 

(placed parallel to shore) and lateral seines that extended from 

each end of the longitudinal seine to shore. All stunned fish 

were collected during three or four successive electroshocking 

passes, species were identified, and lengths and weights were 

recorded. Data from all locations at each site were combined, 

and proportional-reduction methods (Zippin, 1958) were 

used to calculate the numbers and biomass for each species 

population and the total fish community and the corresponding 

95-percent confidence intervals. To standardize the measures 

for each species or for the entire fish community at each 

site, estimates of total density and biomass were divided by 

the total sampling area. Measures of community richness 

(number of species S), species diversity (d), equitability 

(Shannon-Weiner H′), and dominance (Simpson’s C) at 

each site were calculated according to methods described by 

Whittaker (1975).

Potential effects of the releases on fish communities 

were assessed at three Indian River sites (IR01, IR02, and 

IR03) downstream from Lake Abanakee (where adverse 

effects from flow releases should be most evident) and at 

three Hudson River sites (HR02, HR04, and HR05). Any 

effects in the Hudson River should be less than conspicuous 

than the effects in the Indian River because changes in stage 

and flow associated with releases were proportionally smaller 

in the Hudson than in the Indian River; study sites in the 

Hudson River were typically wider than those in the Indian 

River and diluted by relatively large base flows originating 

in unaffected headwaters. Measures of community density, 

biomass, richness, diversity, equitability, and dominance, 

along with the density and biomass of individual species 

populations at the Indian River sites (IR01, IR02, and IR03), 

were compared to those at the Cedar River sites downstream 

of Wakely Dam (CR01, CR02, CR03, and CR04) to quantify 

the potential effects of the releases. Fish communities at 

several sites downstream from both impoundments should 

have been similar because they had comparable drainage 

areas, channel sizes, substrates, and gradients. The sites 

differed mainly with respect to distance downstream from 

each impoundment and river-flow regime: Cedar River sites 

were run-of-the-river, whereas Indian River sites were affected 

by recurring recreational flow releases from Lake Abanakee. 

Fish-community indexes at Hudson River sites HR02, HR04, 

and HR05 (downstream from its confluence with the Indian 

River) were compared with indexes at a control site (HR01) to 

evaluate the potential effects of the releases.

Macroinvertebrate Assemblages

Macroinvertebrates and debris were collected from nine 

sites (CR01, IR01–03, HR01–05) in early August 2005 (fig. 1) 

by using the standard traveling-kick method (Bode and others, 

2002). These nine sites and three additional sites on the Cedar 

River (CR02, CR03, and CR04) were sampled during 2006. 
10 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

At each site, single 5-min. samples were collected in riffles 

that covered a downstream distance of about 5 m. Collection 

nets were rectangular, 23 × 46 cm, with a mesh size of 

0.8 × 0.9 mm. Samples were rinsed in a 500-μm (micrometer) 

mesh sieve and preserved in 95-percent ethanol. At the 

laboratory, 100 specimens were randomly sorted out from the 

debris three times, identified to the lowest possible taxonomic 

level (generally genus or species), and enumerated. This 

triplicate-sorting process generated data for 27 samples from 

2005 and 36 samples from 2006.

Four general macroinvertebrate-community indexes 

or metrics were calculated from each 100-organism sample 

whose members had been identified to the lowest possible 

taxon. Indexes calculated for each site were defined by Novak 

and Bode (1992) and are listed below.

• Total community richness—a measure of the total 

number of macroinvertebrate taxa (generally species) 

found at each site.

• Ephemeroptera-Plecoptera-Trichoptera (EPT) 

richness—a measure of the number of mayfly 

(Ephemeroptera), stonefly (Plecoptera), and caddisfly 

(Trichoptera) taxa found at each site. Species in these 

three orders are widely distributed, generally abundant, 

and tend to be sensitive to variations in water quality.

• Hilsenhoff’s Biotic Index (HBI)—an indicator of 

tolerance to organic enrichment. Sensitive taxa 

have low HBI values, and tolerant taxa have high 

HBI values. 

• Percent model affinity (PMA)—a measure of the 

biological effects of contaminants by comparing the 

benthic macroinvertebrate community at a given 

site to an ideal or model, benthic macroinvertebrate 

community. In riffles of New York streams, this ideal 

community consists of 20 percent Chironomidae, 

10 percent Trichoptera, 40 percent Ephemeroptera, 

5 percent Plecoptera, 10 percent Coleoptera, 5 percent 

Oligocheata, and 10 percent from other orders.

These four indexes were combined into the standard 

New York State Biological Assessment Profile (NYSBAP) 

following methods of Bode and others (2002).

All taxa were also categorized into various functional 

feeding guilds (feeding guilds) according to Merritt and 

Cummins (1996). Relations among macroinvertebrate indexes 

and the NYSBAP, and percentages of functional feeding guilds 

at each site, were evaluated through graphic comparisons and 

multiparametric (ANOVA) analyses to qualify and quantify 

site-to-site differences or similarities and characterize possible 

shifts in community function and overall ecosystem processes 

that might be caused by the releases. Spatial patterns in 

macroinvertebrate-community composition and classifications 

(grouping of sites with similar assemblages) were analyzed 

further by multidimensional scaling (MDS) ordination 

of relative abundance data (square-root transformed) for 

taxa (Shepard, 1962; Kruskal, 1964). The MDS ordination 

generates an arrangement of samples in what is termed 

‘‘species-space,’’ according to the nonparametric ranks of 

their Bray-Curtis similarities (Clarke and Warwick, 2001). 

Bray-Curtis similarities were estimated from the same data 

by using hierarchical cluster (group-average linking) analysis 

and permutation tests of similarity profiles (p less than 0.05) 

(Clarke and Warwick, 2001).

Monitoring Trout Behavior and Temperatures

The primary objectives of the trout-behavior study 

component were to determine whether the releases altered 

the behavior of trout with respect to their level of activity 

and their use of thermal refuges and whether these potential 

effects were biologically relevant in the Indian and Hudson 

Rivers. In addition, the possible effects of recreational releases 

on trout survival were assessed by using indirect data and 

plausible inferences. After the use of thermal refuges by 

stocked trout was confirmed, the effects of releases on usage 

were evaluated through two levels of analysis. For the first 

level, usage of thermal refuges was compared for release days 

and nonrelease days within the same river. If releases had an 

effect on trout behavior, differences in usage between release 

days and nonrelease days would be expected in the Indian and 

Hudson Rivers but not in the run-of-the-river Cedar River. 

Three analytical methods were used to determine if changes 

in trout body temperature were associated with recreational 

releases. For the second level of analysis, indirect effects 

of the releases were compared between the control (Cedar) 

river and each of the affected rivers. If the releases produced 

an effect, then differences in measures such as persistence, 

dispersal, and activity between trout would be expected 

between reference and affected river reaches; however, 

river-specific environmental factors, such as available refuge 

area, could confound these differences. To determine if the 

releases had biologically relevant effects on trout behavior, the 

percentage of trout that were using thermal refuges and also 

affected by the releases were quantified, and the magnitude 

of changes in body temperatures of trout using thermal 

refuges (and not using refuges) were contrasted. Data on trout 

movement and body temperature were collected by using 

radio telemetry with temperature-sensitive transmitters during 

summer field seasons in 2005 and 2006. Although some 

naturalized brown trout are present in the Indian and Hudson 

River study reaches, we assume that the behavior of telemetry 

(study) brown trout is comparable to the behavior of many 

resident brown trout because both groups originate from local 

hatcheries as 2-year olds.

Implanting Radio Transmitters— During both field 

seasons, the trout that were studied consisted of 2-year-old 

domestic-strain brown trout reared in the New York State 

hatchery system. These trout were transported to the Warren 

County Fish Hatchery in Warrensburg, New York, where 

Advanced Telemetry Systems (ATS) radio transmitters were 
Measuring the Effects of Recreational Flow Releases on Habitat and Biological Communities 11

surgically implanted. Mean trout length (± 2 standard errors 

(SE)) was 377.3 ± 6.1 mm in 2005 and 371.7 ± 3.4 mm in 

2006. Implant surgery involved anesthetizing trout, inserting 

a transmitter into the abdominal cavity (using methods similar 

to the shielded-needle technique), and sealing the incision 

with sutures (Ross, 1982; Summerfelt and Smith, 1990). 

Recovering trout were held at the hatchery for 1 week in 2005 

and 2 weeks in 2006 before they were released into study 

reaches. Transmitters were also implanted into control trout 

each season (5 in 2005 and 10 in 2006); these fish were held 

at a local hatchery to assess potential mortality or unusual 

behavior that surgeries may have caused and to assess the 

possibility that the transmitter might be expelled. All control 

trout in 2005 survived and exhibited normal behavior, and no 

trout expelled transmitters until after all field-tracking efforts 

for both years were completed. In 2006, five trout died within 

96 hours of surgery; necropsies revealed punctured organs or 

hemorrhaging. The transmitters from these fish were implanted 

in new trout 1 to 7 days later. The 100-percent survival rate 

for control fish in both 2005 and 2006, and the fact that 

deaths during holding periods occurred within 96 hours of 

surgery, indicate that no surgery-related deaths occurred in 

stocked trout. Radio-tagged trout were stocked into the river 

on July 25, 2005, and on June 14, 2006. Two weeks after the 

initial stocking in 2006, two transmitters taken from trout that 

died in the Indian and Cedar Rivers were implanted into new 

trout from the remaining hatchery population. These newly 

implanted trout were held at the hatchery for 12 days, and then 

stocked into the Hudson River on July 10, 2006, to replenish 

study trout that were dying or disappearing more rapidly than 

those in either the Cedar River or Indian River.

Collection of Trout Temperature Data— The collection 

of multiple body temperatures simultaneously with the precise 

locations for each trout was attempted daily. The primary 

method used to collect data was either by walking or driving 

along banks of the study reaches with a three-element Yagi 

antenna and an ATS RS4500 datalogger (receiver) set to 

aerial-scan mode. The receiver cycled through all transmitter 

frequencies and recorded a temperature for any trout within 

range at a rate of approximately one observation per second. 

The second method (2006 only) was to install a fixed-location 

receiver on the shore of the Hudson River. The scan time and 

observation interval were set to continuously record the body 

temperature every 5 minutes when a trout was within range 

(roughly 1.2 km). For the first 10 days after stocking, the fixed 

receiver was positioned approximately 8 km downstream 

from the stocking location to identify any trout that exited the 

study reach in a nighttime rapid downstream movement, but 

no such actions were recorded. On June 24, 2006, the fixed 

receiver was moved approximately 0.8 km upstream from the 

stocking location and within range of one major and at least 

two minor tributaries. Data collection at the fixed receiver was 

discontinued on July 18, 2006.

Accuracy of Trout Observations—The accuracy of 

observations was subject to systematic and random error. 

Model F1815 and model F1820T radio transmitters were used 

in 2005 and 2006, respectively; these transmitters had factoryspecified accuracy of ± 0.25oC and precision of ± 0.5oC. 

Laboratory tests were conducted on temperature measures 

from the model F1820T transmitter; the average difference 

(± 2 SE) in temperatures recorded by transmitters and a YSI 

(Yellow Springs Instrument Co.) meter was 0.01 ± 0.03oC. The 

mean difference for any individual transmitter was always less 

than 0.2oC, except for one transmitter, for which it was 0.34oC. 

Transmitters were transferred from cool to warm water, 

and the time until temperature stabilized was recorded. On 

average, transmitters warmed to an accuracy of 0.04 ± 0.02oC 

in 154 ± 6 seconds (N=21).

The internal Garmin GPS within each portable ATS 

4500S receiver was reported to be accurate to 15 m (Advanced 

Telemetry Systems, written commun., 2005). Field accuracy 

tests were conducted in 2006 by placing a transmitter in 

the river and observing distances over which the receiver 

could detect the transmitter with only the coaxial cable (no 

antenna) attached. When collecting observations without the 

antenna, receivers could pick up signals from a transmitter 

at distances of 1 to approximately 100 m. By using the gain 

dial to adjust the sensitivity of the receiver, a general sense 

of distances between transmitter and observer was obtained. 

For example, at a gain setting of 3, a transmitter signal could 

not be detected at a distance beyond 30 m. Most observations 

of trout locations were made at gain settings between 1 and 

6; therefore, the accuracy of monitored trout locations was 

considered to be 15 to 100 m. Although accuracies likely were 

similar during both years, transmitter (trout) location errors 

were not estimated in 2005. 

Analysis of Trout Temperature Data— The effects 

of the releases on thermal behavior of tracked trout were 

characterized using three methods. One method, an 

analysis of observations that spanned flow releases (release 

spans),characterized changes in trout body temperature and 

tested whether such changes were associated with the releases. 

In the field, body temperatures for a few individual trout were 

logged by mobile and fixed receivers continuously from just 

before until just after a release event. These release-span 

observations of body temperature from individual trout were 

compiled for both release and nonrelease days. A total of 

31 trout were observed on 38 days for a total of 108 fish-days; 

several trout were observed on more than one day. For each 

fish-day, trout body temperature was monitored 1.5 hours (h) 

prior to, 2 h during, and 1.5 h following the release at a trout’s 

location; data were then extracted and plotted against time. 

Trout temperature records for nonrelease days were identified 

on the basis of average onset times and duration of release 

spans for each trout location. Plots of trout body temperatures 

were visually assessed and classified as displaying no change, 

an increase, or a decrease based on a 0.5oC threshold. Four 

sets of release-span data were collected on the Cedar River, 

but analyses were omitted because only three individual 

trout were observed on 3 consecutive days. A second and 

third set of analyses (methods) were also used to evaluate 

the effects of the releases on thermal behavior of trout. Both 
12 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

compiled and analyzed temperature differences (TD, defined 

as the difference between the temperature of a trout and the 

temperature of the river) between fish and rivers (a) during 

release and nonrelease time blocks (TB) within each river 

and (b) at affected and control river reaches on the same 

days. In 2005 and 2006, all Indian and Hudson River trout 

body-temperature records collected before a release, during 

a release, during the same time periods on nonrelease days, 

and after a release (if daylight permitted—usually only in 

the Indian River) were assessed. Data were divided into six 

4-hour time blocks (TB0 = 0100 – 0459, TB1 = 0500 – 0859, 

TB2 = 0900 – 1259, TB3 = 1300 –1659, TB4 = 1700 – 2059, 

TB5 = 2100 – 0059 Eastern Standard Time) so that most 

release-bubble (episode of peak stage moving through study 

reaches) observations fell within TB2 at the Indian River and 

within TB3 at the Hudson River. During 2006, trout were also 

tracked (observations made) in the Cedar River during time 

blocks TB1 (morning), TB2 (midday), and TB3 (afternoon), 

which correspond to unaffected and affected time blocks 

for study reaches in the other two rivers. All 2005 and 2006 

observations were combined for both analyses. 

For the second method, a set of multilevel models of trout 

and river TDs were assessed for each combination of river and 

time blocks. Repeated measures on the same trout and multiple 

measures on a single day were treated as random effects in 

the models. Fixed effects were incorporated into the model as 

follows: (1) daily variation in TDs, using river temperature 

at time of observation as the metric; (2) daily mean discharge, 

measured at USGS streamgage station 01315500 in North 

River, NY; (3) nearness of trout to a tributary (a trout within 

50 m was consider near, otherwise it was not near); (4) 

release day, classified as either a release or nonrelease day; 

(5) distance of the trout from a river-temperature datalogger; 

and (6) interactions among all combinations of the first four 

variables. Determining interactions between nearness and 

other variables was not possible for the Indian River because 

it had few tributaries, and thus too few observations could be 

made. Aikaike’s Information Criterion (AIC) (Burnham and 

Anderson, 2004) was used to determine which set of plausible 

models for each combination of river and time blocks was best 

supported by the data. This method also determined which 

parameters were most important (predictor weight closest 

to 1) in explaining variations in TD within each model and 

in the entire model set (see Boisvert, 2008, for details). It 

was hypothesized that if the releases had an effect on trout 

thermoregulation, then the variable “release day” would 

be included in the best supported model and would be an 

important parameter within the entire model set. In contrast, 

it was expected that “release day” would not be an important 

parameter for the unaffected Cedar River. Data gathered 

during extreme (flood) flows were excluded from this analysis. 

Multilevel models were analyzed by using the SAS MIXED 

procedure (Littell and others, 1996). A Bonferroni correction 

was used to make multiple comparisons of the least-square 

mean estimates and to examine the magnitudes and directions 

of significant effects.

The third procedure estimated the percentage of trout 

and the percentage of time that thermal refuges were utilized 

to qualify the potential effects (and the biological relevance) 

of the releases on trout behavior. The number of TDs that 

were at least -1oC or -2oC (cooler in trout than in the river) 

was compiled for trout with body temperatures less than 

20oC. The observed TDs represent the potential quality of 

thermal refuges in which a trout may be residing. Elliot (1994) 

concluded that 19oC was the lowest temperature (upper critical 

range) at which normal brown trout behavior is disrupted 

as waters warm. Therefore, analyses herein considered 

temperatures of 20oC and greater to be stressful to trout. 

Counts were grouped by time block and release condition for 

each river to estimate the percentage of trout that were using 

thermal refuges and either were affected or unaffected by 

the releases.

Analysis of Trout Movement— When possible, precise 

daily trout locations were recorded before release time 

blocks so that differences in daily movements on release and 

nonrelease days could be assessed. An internal GPS within 

each portable ATS 4500S receiver automatically logged 

all trout transmitters within range; thus, the coordinates 

represented the location of the observer, but not the trout. 

Observers moved along the river bank and logged the 

trout’s location at a point where the transmitter signal was 

perpendicular to the observer. The observer recorded the 

lowest gain setting at which the signal was detected and, 

thus, the estimated accuracy of the trout’s location. Riverbank locations were transferred to corresponding midchannel 

locations by using GIS software (Manifold) that digitized and 

segmented a river centerline with nodes at 5-m increments. 

A nearest neighbor algorithm was used to translate each 

river-bank location to the nearest center-line node. Despite 

measurement error and data manipulations, the locations were 

sufficiently accurate to place a trout within geomorphic habitat 

units. Precise trout locations were not consistently recorded 

during 2005; therefore, daily trout movements were not 

calculated nor assessed for 2005 observations.

Trout positions relative to initial stocking location 

(meters upstream or downstream) were used to calculate the 

spatial characteristics of trout behavior during 2006. The 5th, 

25th, 50th (median), 75th, and 95th quantiles of total travel 

distances and mean dispersion distances approximately 1 day, 

1 week, 1 month, and 2 months after stocking were estimated. 

Activity was calculated as the average distance trout traveled 

between daily locations (Bettinger and Bettoli, 2002). Only 

observations from consecutive days were used because a 

Spearman’s rank correlation revealed a temporal bias: longer 

movements were correlated with the number of days between 

observations. A Kruskal-Wallis test (Hatcher and Stepanski, 

1994) was used to determine whether activity was different 

between rivers, and multiple comparisons were made using 

Dunn’s test (Zar, 1996).
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 13

Analysis of Persistence and Fate— By definition, 

persistence is equivalent to neither survival nor mortality; 

however, persistence was considered a surrogate for mortality 

for the purposes of this investigation. It was calculated as 

the number of days that each trout remained alive and within 

respective study reaches (Bettinger and Bettoli, 2002). Mean 

persistence was estimated by using the SAS LIFETEST 

procedure, which allows for observations that were identified 

as “censored” (that is, trout that survived beyond the 

conclusion of the study). Mean persistence was compared 

among rivers within each year, and a Wilcoxon statistic was 

used to test homogeneity between survival curves (Allison, 

1995). In this analysis, lost transmitters were treated as an 

outcome of mortality or emigration; that is, the trout were 

removed from the river system by some unknown means. 

Thus, mortality rates based on persistence were expected to be 

biased high and were used only to estimate potential mortality 

and assess relative differences among the three rivers and 

between study years.

Determining the fate of each trout indicates likely causes 

for trout mortality and the degree to which releases contribute 

directly or indirectly to possible morbidity. The fate of each 

trout can be estimated with some degree of confidence on the 

basis of final confirmed or inferred locations of transmitters. In 

many cases, no trout or their remains were ever found with the 

transmitters. Approximately 50 percent of all transmitters were 

recovered, and the final locations of remaining transmitters 

were inferred. The fate of each trout was assigned to one of 

the following categories: (1) “signal lost,” which indicates 

that the signal for the transmitters was no longer detected; 

(2) “in woods,” which describes locations beyond the width 

of the river at the highest summer flood (one trout in this 

category in 2006 had been taken by an angler); (3) “flood 

zone or shallow water,” which describes locations with water 

depth not likely to be accessible to adult trout under base-flow 

conditions, but accessible when flooded during higher flows; 

(4) “midchannel,” which describes locations in the river other 

than shallow water; and (5) “in living trout,” which refers to a 

transmitter that showed evidence (either through its continuing 

activity or by visual observation) of remaining in a living trout 

at the end of the study.

Processing Telemetry Data— The receivers collected 

tens of thousands of records that subsequently required 

additional compilation or vetting to eliminate imprecise, 

duplicate, or spurious data. The first step in cleaning telemetry 

data was to determine the end dates, that is, the first day 

when a trout no longer persisted within a study reach. The 

2006 transmitters were equipped with sensors that produced 

a mortality signal if a transmitter did not move for more than 

8 hours. When a mortality signal was recorded, the end date 

was identified on the basis of prior and current temperature 

and location data. If the location of the transmitter had not 

changed for many days, the end date was the first day that 

the trout was observed at the same location. Similarly, if no 

mortality signal was emitted, and there was no change in 

trout movement from the final observed location, the first 

day at this location was the end date. If the signal indicated 

either by temperature or by location that the transmitter was 

out of the water, the end date was the day this condition was 

first observed. All data collected subsequent to the end date 

for a transmitter were excluded from analyses. Trout body 

temperatures and locations recorded during the 2006 floods 

(when daily discharge averaged more than 2,600 ft3/s at USGS 

station 01315500) were also excluded from most analyses 

summarized herein.

River-temperature data were added; related calculations 

were completed; and time block and release codes were 

applied to the final telemetry dataset to categorize conditions 

and simplify analyses. A median body temperature was 

estimated for each trout during each time block and paired 

with a river temperature from the closest datalogger (at the 

time that the trout’s temperature was logged); individual TDs 

were calculated as the differences between these values. For 

trout in the Indian and Hudson Rivers, body temperatures 

were measured and coded as being under either release or 

nonrelease condition on the basis of stages at the closest 

datalogger, which indicated the presence or absence of 

a release bubble when the trout’s location was recorded. 

Observations were coded “release” only for TB2 on the Indian 

River and for TB3 on the Hudson River during release days. 

The Hudson River dataset also included observations recorded 

by the fixed receiver when manual-tracking data were not 

collected. The resulting file included the following data for 

each trout on a given day: day, river, trout identification 

(ID), time block (a new record for each different time block 

on the same day), time of measurement, trout temperature, 

corresponding river temperature, TD, and location coordinates 

(table 3).

Additional variables were added to this dataset 

(table 4) for analysis of mixed-effects models. These variables 

summarize the (1) total number of days that each trout was 

tracked in each river during each year, (2) percentage of 

tracking done on release days, (3) total trout-sampling events 

(observations of an individual trout temperature during a 

single time block on a given day), and (4) percentage of 

sampling events during a release. The “during release” 

category was not applicable for Cedar River observations 

because there were no flow releases

Effects of Recreational Flow Releases 

on Natural Resources of the Indian and 

Hudson Rivers

Summaries of riverine conditions and the relations 

between, and the differences among, key resources 

are provided in separate sections and in several related 

publications cited as follows.
14 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06 Table 3. Examples of telemetry data logged for trout 151444 on given days and during selected time blocks under release or nonrelease conditions in the Hudson River in June 2006. [EDT, Eastern daylight time; °C, degrees Celsius; release code 1, during release; release code 2, not during release] Date River Trout identification Time block Time (EDT) Release code Trout temperature (°C) River Temperature (°C) Temperature difference (°C) Position1 Easting (meters) Northing (meters) 14–Jun–06 HR 151444 3 14:12:49 2 17.97 17.69 -0.28 576017.9 4845797 16–Jun–06 HR 151444 2 10:31:40 2 18.69 18.27 -0.42 576017.9 4845797 18–Jun–06 HR 151444 2 12:49:10 2 22.77 22.16 -0.61 576024.1 4845796 18–Jun–06 HR 151444 3 16:10:33 1 22.34 21.73 -0.61 20–Jun–06 HR 151444 2 12:59:59 1 22.81 22.21 -0.6 575993.4 4845815 20–Jun–06 HR 151444 3 13:01:04 1 22.81 22.21 -0.6 20–Jun–06 HR 151444 4 18:32:14 2 19.77 21.01 1.24 21–Jun–06 HR 151444 2 12:37:54 2 22.61 21.99 -0.62 576018.0 4845810 21–Jun–06 HR 151444 3 15:19:00 2 23.19 22.62 -0.57 22–Jun–06 HR 151444 2 12:14:01 2 21.02 20.38 -0.64 576507.2 4847487 22–Jun–06 HR 151444 3 13:58:33 1 21.65 20.82 -0.83 23–Jun–06 HR 151444 3 15:19:58 2 23.94 23.01 -0.93 576013.8 4845796 24–Jun–06 HR 151444 4 17:21:00 2 21.51 19.49 -2.02 576012.4 4845822 25–Jun–06 HR 151444 4 17:18:26 2 23.57 22.36 -1.21 575960.8 4845903 26–Jun–06 HR 151444 4 17:15:32 2 20.92 19.49 -1.43 575960.7 4845920

1Position in Universal Transverse Mercator Zone 18 (U18).
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 15

Discharge of the Indian River Below 

Lake Abanakee

In November 2004, a near real-time streamgage (Indian 

River below Lake Abanakee near Indian Lake, USGS station 

01315081) was installed on the Indian River immediately 

downstream from the Lake Abanakee Dam (IR01 in fig. 1). 

Daily mean discharge data during each month in 2005 and 

2006 (tables 5 and 6) show that discharge at IR01 was 

usually high in summer 2006 compared to summer 2005; 

daily mean flows were 259 and 443 ft3/s from June to 

September in 2005 and 2006, respectively. On release days 

during June–September 2005, discharge averaged 180 ft3/s 

immediately before each release, peaked at 1,387 ft3/s during 

releases, and decreased to 127 ft3/s after the spillway gate 

closed. Discharge during the releases increased, usually within 

30 minutes, by an average of 1,207 ft3/s. On release days 

from June to September 2006, discharge averaged 349 ft3/s 

immediately before each release, peaked at 1,410 ft3/s during 

releases, and decreased to 263 ft3/s after the spillway gate 

closed. Discharge after releases decreased by 65 to 70 ft3/s 

(mean 66 ft3/s) and by 63 to 96 ft3/s (mean 80 ft3/s) in 2005 

and 2006, respectively. River discharge at IR01 did not 

recover to prerelease levels until the next release 60 percent of 

the time in 2005 and 46 percent of the time in 2006.

Indian and Hudson River Stages—Stage and water 

temperature were recorded every 15 minutes (except during 

equipment failures) at three sites on the Indian River, five 

sites on the Hudson River, and two sites on Lake Abanakee 

(fig. 1). Average increases in stage from start to peak of release 

on release days were compared to changes during the same 

time interval on nonrelease days to assess the magnitude and 

significance of changes at each site during June to September 

2005 and during the same months in 2006 (tables 7 and 8). 

Monthly mean increases in stage during releases at the three 

Indian River sites ranged from 1.18 to 2.14 ft during 2005 

and from 0.79 to 1.94 ft during 2006. Monthly mean changes 

in stage during releases at sites in the Hudson River ranged 

from 1.14 to 3.15 ft in 2005 and from 0.67 to 1.31 ft during 

2006. Data in figures 4A and 5A depict changes in stage 

during release days on the two rivers, and figures 4B and 5B 

depict changes in stage on nonrelease days. The release effect 

among sites was relatively constant; exceptions occurred at 

IR01, which is directly below the dam, and at HR03, which is 

in a gorge (fig. 6). Significant changes in stage were observed 

at all sites downstream from the dam, but the control site 

HR01 (fig. 1) was not affected because it is upstream from the 

confluence of the Indian and the Hudson Rivers (fig. 6).

After the gate was closed and stage in the Indian River 

downstream of Lake Abanakee dropped below prerelease 

levels, it took 24 hours or more elapsed time before the stage 

returned to levels observed before the gate was first opened. 

In 2005, monthly mean river stages during June, July, August, 

and September decreased by 0.23 to 0.27 ft (mean 0.25 ft) 

below stages prior to the release after the gate was closed. In 

2006, monthly mean river stages during June, July, August, 

and September at the Indian River below Lake Abanakee 

decreased by 0.13 to 0.33 ft (mean 0.23 ft) below stages prior 

to the release after the gate was closed.

Lake Abanakee Stage—The mean stage on release 

and on nonrelease days was calculated for AB01 and AB02 

in 2005 and for AB02 in 2006 (table 9). Decreases in lake 

stage associated with releases at the dam were consistently 

about 0.30 ft. A drawdown of almost 2 ft occurred in October 

2005 when the spillway gate reportedly failed in the open 

position (fig. 7). At the end of June and beginning of July 

2006, the gate at Abanakee Dam was intentionally left open 

for several days to alleviate flooding (fig. 8). The lake did 

not fully rebound prior to the next release for several days 

during August 2006 (fig. 9). Between July 2 and October 

2, 2005, the lake always recovered to at least 75 percent 

of the prerelease stage, had an average recovery before the 

next release of 91 percent of the prerelease stage, and fully 

recovered to 100 percent of the prerelease stage 50 percent 

Table 4. The scope of the trout telemetry sampling effort in 2005 and 2006. 

[Individual trout were observed up to three times per day; releases did not occur during flood stages]

Study reach 

and 

reach number

Total number 

of observations

Total number 

of days trout 

were tracked

Percentage of days 

trout were tracked 

on release dates 

Number (and 

percentage) 

of observations

on release days 

2005

Indian River IR01–IR03 200 17 47 83 (42)

Hudson River HR04–HR05 108 15 60 70 (65)

2006

Indian River IR01–IR03 870 45 47 393 (45)

Hudson River HR04–HR05 676 50 48 233 (34)

Cedar River CR01–CR03 1,045 46 46 329 (31)
16 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

Table 5. Daily discharges in cubic feet per second on the Indian River below Lake Abanakee near Indian Lake (site IR01) for 

November 2004 through September 2005 and total monthly discharges with daily mean, maximum, and minimum for each month. 

[Unit conversions are shown in the conversion tables at the front of the report. E, estimated; --, no measurement made; * denotes value calculated from the 

incomplete record for November 2004]

Day November December January February March April May June July August September

1 --- 544 612 173 174 785 1,340 234 170 143 391

2 --- 644 617 242 171 430 1,230 235 314 218 280

3 --- 589 630 259 166 1,380 1,120 251 373 145 312

4 --- 566 635 262 164 1,090 985 245 297 245 258

5 194 655 622 261 162 606 951 214 236 170 242

6 205 704 609 261 162 416 592 183 193 241 208

7 E230 661 601 260 162 427 265 183 324 225 217

8 232 690 587 263 174 501 197 159 257 144 270

9 231 728 580 267 178 485 232 226 330 196 201

10 254 736 572 278 172 411 255 264 301 135 282

11 314 757 561 277 170 359 279 261 255 249 241

12 328 744 559 271 171 314 252 238 348 173 167

13 328 707 559 270 168 283 200 187 255 225 205

14 326 674 665 270 165 249 203 210 288 181 216

15 330 641 736 281 164 226 173 196 130 88 264

16 342 623 686 286 160 163 160 405 230 199 195

17 368 613 644 288 156 155 139 1,350 212 79 266

18 360 599 603 284 155 129 134 1,430 115 188 236

19 351 593 574 278 155 155 133 1,010 192 106 182

20 342 586 562 275 155 101 129 1,080 160 189 236

21 335 574 551 275 158 143 161 712 256 168 203

22 330 570 539 271 159 181 154 294 189 100 260

23 326 589 536 269 160 384 150 541 249 209 186

24 334 775 528 266 168 1,420 158 317 218 87 253

25 478 782 524 265 175 1,160 218 310 145 215 239

26 548 717 522 263 175 1,100 265 193 241 78 188

27 496 674 519 249 185 1,640 262 64 185 174 285

28 486 637 513 186 186 1,760 275 206 258 180 219

29 562 620 488 --- 239 1,730 258 120 176 102 266

30 524 607 424 --- 280 1,450 245 233 231 212 219

31 --- 598 200 --- 272 --- 218 --- 258 343 ---

Total 9,154* 20,197 17,558 7,350 5,461 19,633 11,333 11,551 7,386 5,407 7,187

Mean 352* 652 566 262 176 654 366 385 238 174 240

Maximum 562* 782 736 288 280 1,760 1,340 1,430 373 343 391

Minimum 194* 544 200 173 155 101 129 64 115 78 167
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 17

Table 6. Daily discharges on the Indian River below Lake Abanakee near Indian Lake (site IR01) for October 2005 through September 

2006 and total monthly mean discharges with daily mean, maximum, and minimum for each month. 

[Unit conversions are shown in the conversion tables at the front of the report. --, no measurement made]

Day October November December January February March April May June July August September

1 283 749 935 563 813 648 270 365 491 1,840 653 383

2 252 813 751 541 792 640 302 288 382 1,460 341 453

3 191 770 677 526 824 638 300 271 674 896 626 414

4 255 702 629 514 951 630 335 312 1,030 1,390 438 391

5 195 656 601 509 1,210 624 358 351 954 1,170 373 358

6 284 627 577 502 1,210 619 308 240 756 913 290 286

7 292 631 556 492 1,050 614 305 270 558 718 242 245

8 687 609 537 488 931 608 253 281 726 811 303 147

9 742 618 533 485 862 605 256 597 479 804 233 210

10 669 926 529 480 634 609 215 794 578 754 286 196

11 255 811 518 477 701 637 199 754 637 756 212 138

12 298 673 514 497 740 652 167 245 571 850 224 238

13 490 646 509 511 729 689 179 332 540 1,080 162 161

14 545 617 501 540 719 856 235 572 536 853 66 222

15 1,080 617 492 636 708 599 208 808 458 858 156 147

16 1,170 993 506 608 701 296 163 1,140 381 852 95 220

17 773 1,020 502 577 740 246 186 1,200 258 724 146 205

18 701 731 495 980 766 229 174 1,100 209 783 43 150

19 661 684 492 1,550 737 204 129 1,130 192 742 131 238

20 615 651 488 1,340 716 181 119 1,060 269 610 206 200

21 583 617 484 1,150 699 135 138 977 234 256 171 261

22 563 598 481 1,080 723 136 136 714 342 277 293 189

23 597 586 477 998 703 137 695 380 340 354 232 255

24 640 565 475 926 681 134 1,890 433 392 329 263 231

25 750 553 480 885 675 137 1,760 424 281 406 202 177

26 989 542 563 712 671 144 1,400 410 188 588 275 250

27 894 533 588 749 662 144 1,220 343 704 607 279 171

28 784 529 565 778 654 147 922 280 2,160 478 226 211

29 712 573 549 775 --- 156 943 252 3,200 779 279 212

30 678 843 579 785 --- 170 904 272 2,500 729 215 270

31 700 --- 571 807 --- 185 --- 735 --- 590 298 ---

Total 18,328 20,483 17,154 22,461 22,002 12,449 14,669 17,330 21,020 24,257 7,959 7,229

Mean 591 683 553 725 786 402 489 559 701 782 257 241

Maximum 1,170 1,020 935 1,550 1,210 856 1,890 1,200 3,200 1,840 653 453

Minimum 191 529 475 477 634 134 119 240 188 256 43 138
18 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06 Table 7. Mean change in river stage from start of release to peak flow on release days and during the same interval on nonrelease days and number of release and nonrelease days at eight sites on the Indian and Hudson Rivers in the Adirondack Mountains, New York, for each month during June–September, 2005. [Mean change in river stage, in feet, is the first number, and the number of observations is the second number (in parentheses). Locations of study sites are shown in figure 1; unit conversions are shown in the conversion tables at the front of the report. Site codes are listed in table 1. Mean monthly change in stage was significant (p-value < 0.001) at all sites except HR01. na, data not available] Period Flow condition Study sites IR01 IR02 IR03 HR01 HR02 HR03 HR04 HR05 June release nonrelease 1.93 (20) -.01 (10) 1.26 (4) 0 (2) na na na na na na July release nonrelease 1.95 (18) 0 (13) 1.23 (18) 0 (13) 1.22 (17) 0 (12) 0 (18) 0 (13) 1.14 (18) .01 (13) 2.43 (18) 0 (13) 1.17 (18) 0 (13) 1.24 (18) 0 (13) August release nonrelease 2.14 (17) .01 (14) 1.39 (17) .01 (14) 1.33 (17) .01 (14) 0 (17) 0 (14) 1.45 (10) .01 (8) 3.15 (14) .01 (8) 1.58 (17) .01 (14) 1.57 (15) 0 (12) September release nonrelease 1.89 (17) 0 (13) 1.18 (17) 0 (13) 1.48 (17) .01 (13) 0 (17) 0 (13) 1.17 (16) .02 (14) 2.40 (17) .02 (13) 1.15 (17) 0 (13) 1.22 (17) .01 (13) For all months release nonrelease 1.98 (72) 0 (50) 1.27 (56) .01 (42) 1.34 (51) .01 (39) 0 (52) 0 (40) 1.22 (44) .01 (35) 2.63 (49) .01 (34) 1.30 (52) 0 (40) 1.33 (50) 0 (38) Table 8. Mean change in river stage from start of release to peak flow on release days and during the same interval on nonrelease days and number of release and nonrelease days at eight sites on the Indian and Hudson Rivers in the Adirondack Mountains, New York, for each month during June–September, 2006. [Mean change in river stage in feet is the first number, and the number of observations is the second number (in parentheses). Locations of study sites are shown in figure 1; unit conversions are shown in the conversion tables at the front of the report. Site codes are listed in table 1. Mean monthly change in stage was significant (p-value < 0.001) at all sites except HR01. na; data not available] Period Flow condi- tion Study site IR01 IR02 IR03 HR01 HR02 HR03 HR04 HR05 June release nonrelease 1.42 (23) .08 (7) .79 (23) .02 (7) 1.12 (23) .07 (7) 0.0 (23) .02 (7) .68 (19) .01 (2) na .76 (23) .02 (7) .76 (23) .06 (5) July release nonrelease 1.28 (16) -.04 (15) .79 (16) -.02 (15) .94 (16) -.02 (15) 0.0 (16) -.01 (15) na na .67 (16) -.02 (15) na August release nonrelease 1.94 (18) .01 (13) 1.27 (18) .01 (13) 1.35 (18) .01 (13) 0.0 (18) 0.0 (13) na na 1.24 (18) .01 (13) na September release nonrelease 1.88 (18) .01 (12) 1.23 (16) 0.0 (11) 1.30 (15) 0.00 (10) 0.0 (12) 0.0 (8) na na 1.31 (15) 0.0 (10) na Mean for 

all months

releasenonrelease

1.63 (75)

0.0 (47)

1.00 (73)

0.0 (46)

1.18 (72)

.01 (45)

0.0 (69)0.0 (43)

na na .97 (72)

0.0 (45)

na
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 19

of the time; between July 6 and September 27, 2006, the lake 

always recovered to at least 84 percent of the prerelease stage, 

had an average recovery before the next release of 98 percent 

of the prerelease stage, and fully recovered to 100 percent of 

the prerelease stage 58 percent of the time. In 2005 recovery 

times ranged from 10 to 48 hours with an average recovery 

time of 31 hours, and in 2006 recovery times ranged from 6 to 

48 hours with an average recovery time of 29 hours. 

Recharge times in Lake Abanakee were initially 

hypothesized to depend mainly on inflows from Indian 

Lake. Stages at Indian Lake, Lake Abanakee, and IR01 

between July 1 and August 1, 2005 (fig. 10A), and July 1 and 

August 1, 2006 (fig. 10B), however, indicate that precipitation 

and other inflows had a strong effect on stage-rebound times in 

Lake Abanakee. A more comprehensive analysis of gaged and 

ungaged inflows, precipitation, lake stage, and flow releases 

would be needed to fully characterize the effects of releases on 

recharge in Lake Abanakee.

River Temperatures

Temperature data were collected at three sites on the 

Indian River and at five sites on the Hudson River (fig. 1) to 

help quantify the thermal effects of the releases from Lake 

Abanakee. The mean changes in stream temperature from the 

start to the peak of releases on release days were compared 

to the mean changes for the same time period on nonrelease 

days to assess the magnitudes and significances of releases 

on thermal conditions at each study site during the months of 

June, July, August, and September in 2005 and 2006 (tables 

10 and 11). Analysis of the pooled data for the 4 months in 

2005 indicated that dam releases caused small but significant 

decreases in temperature at IR01 and IR02 and possibly 

reduced the rate of diel temperature increases at IR03, HR02, 

and HR04 (table 10). Analysis of the pooled 2006 data showed 

-0.5

0.0

0.5

1.0

1.5

2.0

EASTERN STANDARD TIME

A Indian River stage on a release day

-0.5

0.0

0.5

1.0

1.5

2.0

CHANGE IN STAGE, IN FEET

EASTERN STANDARD TIME

B Indian River stage on a nonrelease day

IR03 IR02 IR01

EXPLANATION

6:00

6:45

7:30

8:15

9:00

9:45

10:30

11:15

12:00

12:45

13:30

14:15

15:00

15:45

16:30

17:15

18:00

18:45

19:30

6:00

6:45

7:30

8:15

9:00

9:45

10:30

11:15

12:00

12:45

13:30

14:15

15:00

15:45

16:30

17:15

18:00

18:45

19:30

A Hudson River stage on a release day

B Hudson River stage on a nonrelease day

HR01 HR02 HR03 HR04 HR05

CHANGE IN STAGE, IN FEET

EASTERN STANDARD TIME

EASTERN STANDARD TIME

EXPLANATION

0.0

0.5

1.0

1.5

2.0

3.0

2.5

0.0

0.5

1.0

1.5

2.0

3.0

2.5

6:00

6:45

7:30

8:15

9:00

9:45

10:30

11:15

12:00

12:45

13:30

14:15

15:00

15:45

16:30

17:15

18:00

18:45

19:30

6:006:457:308:159:009:45

10:3011:1512:0012:4513:3014:1515:0015:4516:3017:1518:0018:4519:30

Figure 5. Graphs showing cChange in stage at five Hudson 

River sites A, on July 7, 2005, a release day, and B, on July 

8, 2005, a nonrelease day, Adirondack Mountains, New York. 

Locations of study sites are shown in figure 1; study-site codes 

are listed in table 1.

Figure 4. Graphs showing cChange in stage at three Indian 

River sites A, on July 7, 2005, a release day, and B, on July 8, 2005, 

a nonrelease day, Adirondack Mountains, New York. Locations 

of study sites are shown in figure 1; study-site codes are listed in 

table 1.
20 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

Figure 6. Graph showing cChange in stage at eight study sites on the Indian and Hudson Rivers, Adirondack 

Mountains, New York, on release and nonrelease days from July 1 to August 1, 2005. Locations of study sites are shown 

in figure 1; study-site codes are listed in table 1.

STUDY-SITE CODE

CHA

N

GE IN ST

A

GE, IN FEET

0

1

2

3

IR01 IR02 IR03 HR01 HR02 HR03 HR04 HR05

EXPLANATION

75th percentile

 25th percentile

Mean

Largest value

Smallest value

Median

4

Release

Nonrelease

Table 9. Mean change in the stage of Lake Abanakee from start of release until closing of the spillway gate on release days 

and number of release and nonrelease days at two study sites in the Adirondack Mountains, New York, and during the same 

interval on nonrelease days during June–September 2005 and at one site during June–September 2006. 

[Mean change in lake stage in feet is the first number, and the number of observations is the second number (in parentheses). Locations of study sites 

are shown in figure 1; unit conversions are shown in the conversion tables at the front of the report.. Site codes are listed in table 1. Mean monthly 

change in lake stage was significant (p-value < 0.001) at all sites except HR01. na, data not available]

Period Flow condition

Study site and year

2005 2006

AB01 AB02 AB02

June release

nonrelease

-0.32 (4)

0.02 (2)

na -0.26 (23)

0.02 (7)

July release

nonrelease

-0.30 (15)

0.01 (12)

-0.31 (18)

0.01 (13)

-0.23 (16)

0.0 (15)

August release

nonrelease

-0.32 (7)

0.01 (7)

-0.34 (12)

0.01 (10)

-0.32 (18)

0.01 (13)

September release

nonrelease

-0.29 (5)

0.0 (1)

-0.29 (17)

0.01 (13)

-0.32 (16)

0.0 (11)

For all months release

nonrelease

-0.31 (31)

0.01 (22)

-0.31 (47)

0.01 (36)

-0.28 (73)

0.01 (46)
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 21

OCTOBER 2005

1 5 9 13 17 21 25

LAKE ABANAKEE STAGE, IN FEET

0.0

0.5

1.0

1.5

2.0

2.5

29

25 29 03 07 11 15 

LAKE ABABANAKEE STAGE, IN FEET

0. 5

1. 0

1. 5

2. 0

2. 5

3. 0

3. 5

4. 0

JUNE 2006 JULY 2006

Figure 8. Graph showing lLake stage at Lake Abanakee at Route 28 bridge near Indian Lake (AB02), 

Adirondack Mountains, New York, during June and July 2006. Location of AB02 is shown in figure 1; 

study-site codes are listed in table 1.

Figure 7. Graph showing lLake stage at Lake Abanakee at Route 28 bridge near Indian Lake (AB02), 

Adirondack Mountains, New York, during October 2005. Location of AB02 is shown in figure 1; studysite codes are listed in table 1.
22 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

significant decreases in temperature during releases at IR01, 

significantly delayed diel temperature increases at IR02, and 

possibly moderated diel temperature increases at IR03 and 

HR04 (table 11). Examination of changes in water temperature 

over a 3-day period (2 nonrelease days and 1 release day) 

in the Indian and the Hudson Rivers showed that releases 

lowered temperature in the Indian River (fig. 11) and delayed 

and(or) reduced daily temperature increases in the Hudson 

River (fig. 12). Lower mean and median daily temperatures 

at all sites on release days than on nonrelease days between 

July 1 and August 1, 2005, (fig. 13) provide additional 

evidence for a cooling effect. The control site (HR01) 

exhibited no significant temperature differences between 

release days and nonrelease days. Decreases in temperature at 

several sites affected by releases were very small, indicating 

that the thermal changes would have no direct (positive or 

negative) effect on survival of resident trout. Regardless of 

releases, water temperatures at all study sites commonly 

exceeded the threshold (20°C) known to be stressful to 

brown trout. River-water temperatures were higher at all 

sites in summer 2005 than in summer 2006: monthly mean 

temperatures were 1.1, 1.6, and 2.8°C greater during July, 

August, and September 2005 than during the same periods 

in 2006. The maximum water temperature for the period of 

record at Indian River below Lake Abanakee was 26.5°C on 

July 18, August 9, and August 10, 2005. Daily maximum, 

minimum, and mean temperatures for each site are available 

in the 2005 and 2006 New York Annual Water-Data Reports 

for Eastern New York, excluding Long Island (http://ny.water.

usgs.gov/htmls/pub/data.html). 

Temporal and Spatial Patterns in Temperature of 

the Hudson River 

Important temporal and spatial patterns in river 

temperatures from aerial infrared (IR) data are summarized 

below; more complete analyses of thermal-imaging results 

are provided in Ernst and others (in press). The longitudinal 

temperature profiles constructed for three periods over the 

course of a release day (fig. 14A) show that river temperatures 

increased unevenly during the day. During the first flight 

(10:12 Eastern Standard Time (EST)), when the high-water 

bubble covered the river between kilometers 1 and 5, most 

surface-water temperatures were below 22°C and generally 

decreased downstream (fig. 14A). During the second flight 

(12:39 EST), when the high-water bubble covered the river 

between kilometers 4 and 19, surface temperatures were near 

22°C, although middle reaches between kilometers 6 and 

18 containing the bubble were slightly cooler than the upper 

reaches between kilometers 1 and 4 and the lower reaches 

AUGUST 2006

5 13 21 29 

LAKE ABANAKEE STAGE, IN FEET

0. 8

1. 0

1. 2

1. 4

1. 6

1. 8

2. 0

2. 2

2. 4

1 9 17 25

Figure 9. Graph showing lLake stage at Lake Abanakee at Route 28 bridge near Indian Lake 

(AB02), Adirondack Mountains, New York, during August 2006. Location of AB02 is shown in figure 1; 

study-site code is listed in table 1.
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 23

A July 2005

JULY 2005

1 5 13 21 29

INDIAN LAKE STAGE, IN FEET

30

31

32

33

34

35

36

AB02 STAGE, IN FEET

1. 0

1. 5

2. 0

2. 5

3. 0

IR01 STAGE, IN FEET

1

2

3

4

5

6

7

B July 2006

JULY 2006

INDIAN LAKE STAGE, IN FEET

30

31

32

33

34

35

36

AB02 STAGE, IN FEET

1. 0

1. 5

2. 0

2. 5

3. 0

IR01 STAGE, IN FEET

1

2

3

4

5

6

7

Indian Lake stage

AB02 stage

IR01 stage 

EXPLANATION

9 17 25

1 5 9 13 17 21 25 29

Figure 10. Graphs showing sStage at Indian Lake, Lake Abanakee (AB02), and Indian River (IR01), Adirondack 

Mountains, New York, during A, July 2005, and B, July 2006. Locations of study sites are shown in figure 1; study-site 

codes are listed in table 1.
24 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06 Table 10. Mean change in temperature from start of release to peak flow on release days and during the same time period on nonrelease days and number of release and nonrelease days at eight sites on the Indian and Hudson Rivers in the Adirondack Mountains, New York, during June–September 2005. [Mean change in temperature, in degrees Celsius, is the first number, and the number of observations in days, is the second number (in parentheses). Locations of study sites are shown in figure 1; study-site codes are listed in table 1. Boldface

p-value (< 0.05) indicates significant changes in temperature. na, not available]

Period Type of day Study sites IR01 IR02 IR03 HR01 HR02 HR03 HR04 HR05

June release

nonrelease

-0.60 (20)

0.16 (10)

p<0.001

-0.61 (4)

0.22 (2)

p = 0.022

na na na na na na

July release

nonrelease

-0.40 (18)

0.12 (13)

p<0.001

-0.24 (18)

0.15 (13)

p<0.001

0.05 (17)0.20 (12)

p = 0.047

na 0.17 (18)

0.17 (13)

p = 0.921

0.64 (18)0.47 (13)

p = 0.097

0.08 (18)0.23 (13)

p = 0.104

0.18 (18)0.21 (13)

p = 0.819

August release

nonrelease

-0.21 (17)

0.21 (14)

p<0.001

0.11 (17)0.20 (14)

p = 0.065

0.54 (17)0.75 (14)

p = 0.213

0.50 (15)0.42 (12)

p = 0.411

0.18 (9)0.48 (7)

p = 0.002

0.59 (14)0.49 (8)

p = 0.403

0.01 (17)0.15 (14)

p = 0.029

0.39 (15)0.08 (12)

p = 0.078

September release

nonrelease

-0.04 (17)

0.19 (13)

p<0.001

0.14 (17)0.19 (13)

p = 0.088

0.44 (17)0.38 (13)

p = 0.577

0.39 (12)0.56 (8)

p = 0.232

0.49 (4)0.18 (6)

p = 0.014

0.44 (17)0.43 (13)

p = 0.878

0.02 (17)0.20 (13)

p = 0.007

-0.05 (17)

0.02 (13)

p = 0.164

Mean for 

all months

releasenonrelease

-0.33 (72)

0.17 (50)

p<0.001

-0.04 (56)

0.18 (42)

p<0.001

0.34 (51)0.46 (39)

p = 0.162

0.45 (27)0.48 (20)

p = 0.757

0.21 (31)0.26 (26)

p = 0.368

0.56 (49)0.46 (34)

p = 0.096

0.04 (52)0.19 (40)

p<0.001

0.16 (50)0.10 (38)

p = 0.401
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 25 Table 11. Mean change in temperature from start of release to peak flow on release days and during the same time period on nonrelease days and number of release and nonrelease days at eight sites on the Hudson and Indian Rivers in the Adirondack Mountains, New York, during June–September 2006. 

[Mean change in temperature, in degrees Celsius, is the first number, and the number of observations in days, is the second number (in parentheses). Locations of study sites are shown in figure 1; studysite codes are listed in table 1. Boldface

p-value (< 0.05) indicates significant changes in temperature. na, not available] 

Period Type of day Study sites IR01 IR02 IR03 HR01 HR02 HR03 HR04 HR05

June

releasenonrelease

-0.15 (23)

0.14 (7)

p = 0.001

-0.06 (23)

0.18 (7)

p = 0.008

0.02 (23)0.17 (7)

p = 0.019

0.23 (23)0.18 (7)

p = 0.716

0.22 (19)0.47 (2)

p = 0.033

na 0.19 (23)

0.09 (7)

p = 0.183

0.19 (23)0.14 (5)

p = 0.568

July

releasenonrelease

-0.05 (16)

0.08 (15)

p<0.001

0.03 (16)0.14 (15)

p = 0.003

0.04 (16)0.21 (15)

p = 0.003

0.29 (16)0.30 (15)

p = 0.949

na na 0.17 (16)

0.32 (15)

p = 0.064

na

August

releasenonrelease

-0.05 (18)

0.18 (13)

p<0.001

0.20 (18)0.23 (13)

p = 0.634

0.44 (18)0.34 (13)

p = 0.281

0.20 (18)0.29 (13)

p = 0.179

na na 0.05 (18)

0.37 (13)

p<0.001

0.38 (10)0.36 (7)

p = 0.946

September

releasenonrelease

-0.05 (18)

0.15 (12)

p<0.001

0.04 (16)0.25 (11)

p = 0.003

0.24 (15)0.29 (10)

p = 0.642

0.14 (17)0.13 (11)

p = 0.686

na na -0.02 (15)

0.13 (10)

p = 0.116

0.27 (15)0.51 (10)

p = 0.155

Mean for 

all months

releasenonrelease

-0.08 (75)

0.14 (47)

p<0.001

0.05 (73)0.20 (46)

p<0.001

0.17 (72)0.26 (45)

p = 0.079

0.22 (74)0.24 (46)

p = 0.616

na na 0.11 (72)

0.26 (45)

p<0.001

0.25 (48)0.38 (22)

p = 0.141
26 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

JULY 2005

18 19 20 21 

INDIAN RIVER TEMPERATURE, IN DEGREES CELSIUS

23

24

25

26

27

28

IR01

IR02

IR03

JULY 2005

18 19 20 21 

HUDSON RIVER TEMPERATURE, IN DEGREES CELSIUS

23

24

25

26

27

28

HR02

HR03

HR04 

HR05

Figure 11. Graph showing cChange in temperature of the Indian River at three study sites in the 

Adirondack Mountains, New York, from July 18 to July 21, 2005. Dotted lines represent temperature recorded 

during a release. Locations of study sites are shown in figure 1; study-site codes are listed in table 1.

Figure 12. Graph showing cChange in temperature of the Hudson River at four sites, in the Adirondack 

Mountains, New York, from July 18 to July 21, 2005. Dotted lines represent temperatures recorded 

during a release. Locations of study sites are shown in figure 1; study-site codes are listed in table 1.
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 27

between kilometers 20 and 27 (fig. 14B). During the third 

flight (15:42 EST), most surface temperatures were above 

22°C when the high-water bubble covered the river between 

kilometers 16 and 27. The middle reaches were cooler, and 

the upper reaches were much warmer than other reaches 

(fig. 14C). Thalweg temperatures, used for constructing the 

longitudinal temperature profiles, were generally lower than 

water temperatures along the stream bank during the first 

two flights, although thalweg temperatures and stream-bank 

temperatures were similar during the last flight. All three 

flights recorded many spikes and dips in temperature along the 

thalweg; although either type of change may reflect spurious 

data caused by such irregularities as exposed rocks, only the 

low dips that might indicate cold-water refuges for trout were 

assessed. No cool-water tributaries below the Boreas River 

affected the longitudinal temperature profile (fig. 14), probably 

because inflows along river banks were too small to affect 

temperatures near the thalweg.

An analysis of 1-km river sections showed that the 

largest areas of potential thermal refuge (areas where the 

water temperature was below the median for that section) 

were available to trout during the morning flight (10:12 EST); 

4.1 percent (61,277 m2) of surface water was at least 1oC 

cooler than the median river temperature. Most of the coldest 

refuge area was in the first 4 km of the 27-km reach and was 

measured during passage of the high-water bubble (table 12); 

0.7 percent (781 m2) of surface water was at least 3°C cooler 

than the median temperature, but some rocky banks may have 

been misidentified because of shading. Water temperatures 

measured during the midday flight (12:39 EST) were warmer 

and offered fewer potential refuges along the river: only 

0.4 percent (6,460 m2) of surface water was at least 1oC cooler 

than the median temperature, and no water was 3oC cooler 

than the median (table 12). A few potential refuge areas were 

available in several 1-km sections: six of the eight 1-km 

sections had up to 30 m2 of refuge area when the high-water 

bubble affected the reach. River temperatures measured during 

the afternoon flight (15:42 EST) were warmer still, but more 

refuge area was available than at midday. Areas of water 

that were at least 1oC or cooler than the median temperature 

covered 0.9 percent (13,792 m2) of the river surface. Most 

1-km sections within the afternoon high-water bubble had 

little or no available refuge area when the high-water bubble 

affected the reach (table 12).

During the morning flight, the riparian vegetation on the 

east river bank of all 1-km river sections that ran north-south 

W

A

TER TEMPERA

T

URE, NI DEGREES CELSIUS

20

22

24

26

28

IR01 IR02 IR03 HR02 HR03 HR04 HR05

STUDY-SITE CODE

EXPLANATION

75th percentile

25th percentile

Mean

Largest value

Smallest value

Median

Release

Nonrelease

18

Figure 13. Graph showing cChange in temperature at eight study sites on the Indian and Hudson Rivers in the 

Adirondack Mountains, New York, on release and nonrelase days from July 1 to August 1, 2005. Locations of study sites 

are shown in figure 1; study-site codes are listed in table 1.
28 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

18

20

22

24

26

28

0 5 10 15 20 25 30

DISTANCE DOWNSTREAM FROM LAKE ABANAKEE DAM,

IN KILOMETERS 

TEMPERATURE OF SURFACE WATER, IN DEGREES CELSIUS 

A 10:12 EST

B 12:39 EST

C 15:42 EST

IR01 HR05

HR04

HR03

HR02

IR02

IR03

Boreas River inflow

Raquette Brook inflow

Aldous Brook inflow

Thirteenth

Lake Outflow

Deer Creek Inflow

18

20

22

24

26

28

18

20

22

24

26

28

IR01

HR04

30

EXPLANATION

Inflow point from cold-water tributary along river

Temperature during release and site identifier

Temperature during base flow and site identifier

High water bubble

Base flow

Reference temperature

Figure 14. Graphs showing lLongitudinal temperature profiles of the three Indian Rivers study sites IR01–IR03 and Hudson 

River study sites HR02–HR05 in the Adirondack Mountains, New York, at A, 10:12, B, 12:39, and C, 15:42 Eastern Standard 

Time (EST) during release and nonrelease flows on July 25, 2005; mean temperature at the seven study sites from July 21, 

2005 through September 21, 2005, on release and nonrelease days; and inflow points for five cool-water tributaries.
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 29

Table 12. Median temperature for each 1-kilometer section and refuge areas 1, 2., and 3oC below the median temperature 

for that section during three flights along the 27-kilometer reach of the Indian and Hudson Rivers from the outflow point of the 

Abanakee Dam to North Creek, Adirondack Mountains, New York, July 25, 2005.

[Flight 1 aloft from 10:12 to 10:55 EDT; flight 2 aloft from 12:39 to 13:14 EST; flight 3 aloft from 15:42 to 16:05 EDT. Sections of the river under the 

high-water bubble are highlighted. Locations of study sites are shown in figure 1; unit conversions are shown in the conversion tables at the front of the 

report. Site codes are listed in table 1. oC, degrees Celsius]

Flight 1

Section

(kilometers from 

outflow point)

Total area

(square meters)

Median 

temperature 

(°C)

Refuge area below median temperature (square meters)

1oC 2oC 3oC

1 23,843 20.7 2,169 808 73

2 22,343 19.9 2,871 1,162 4

3 44,379 20 3,170 1,033 457

4 25,053 20.6 3,069 850 247

5 50,744 20.6 1,291 124 0

6 60,802 20 946 253 0

7 57,194 19.6 2,284 579 1

8 61,213 19.6 2,027 379 1

9 61,091 19.8 166 15 0

10 52,149 19.5 3,508 507 1

11 43,962 19.4 868 51 0

12 49,621 19.5 354 49 0

13 44,774 19.7 580 32 0

14 47,229 19.7 3,075 901 28

15 58,242 19.6 2,951 1,285 50

16 5,557 20.1 344 177 6

17 56,832 20.1 116 6 0

18 62,941 19.9 846 118 0

19 69,630 19.8 2,134 397 2

20 77,170 19.7 9,383 442 7

21 63,808 19.7 2,797 599 11

22 71,964 19.7 4,937 576 5

23 95,715 19.4 2,920 121 0

24 86,914 19.2 2,922 103 0

25 77,398 19.4 4,260 223 0

26 74,663 19.2 570 2 0

27 53,488 19.1 719 93 0

Mean temperature 19.7

Total area of the

27 sectors

1,498,719

Total area 1–3°C 

below mean 

temperature 

(percentage of total 

27-kilometer reach)

61,277 (4.09) 10,885 (0.72) 893 (0.060)
30 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

Table 12. Median temperature for each 1-kilometer section and refuge areas 1, 2, and 3oC below the median temperature for 

that section, during three flights along the 27-kilometer reach of the Indian and Hudson Rivers from the outflow point of the 

Abanakee Dam to North Creek, Adirondack Mountains, New York, July 25, 2005.—Continued

[Flight 1 aloft from 10:12 to 10:55 EDT; flight 2 aloft from 12:39 to 13:14 EST; flight 3 aloft from 15:42 to 16:05 EDT. Sections of the river under the 

high-water bubble are highlighted. Locations of study sites are shown in figure 1; unit conversions are shown in the conversion tables at the front of the 

report. Site codes are listed in table 1. oC, degrees Celsius]

Flight 2

Section

(kilometers from 

outflow point)

Total area

(square meters)

Median 

temperature

(°C)

Refuge area below median temperature (square meters)

1oC 2oC 3oC

1 24,314 22.1 89 0 0

2 22,327 21.9 57 0 0

3 44,380 21.8 4 0 0

4 25,025 21.9 12 0 0

5 50,741 21.9 100 0 0

6 60,772 22 94 0 0

7 57,199 21.7 386 50 0

8 61,185 21.8 288 13 0

9 60,983 21.6 113 25 0

10 52,040 21.4 71 2 0

11 43,962 21 120 0 0

12 49,535 20.8 14 0 0

13 44,699 21.1 0 0 0

14 26,955 21.2 469 0 0

15 58,122 21.1 209 7 0

16 5,519 21.5 0 0 0

17 56,731 21.6 4 0 0

18 62,817 21.7 30 0 0

19 69,512 21.8 283 0 0

20 77,139 21.9 383 0 0

21 63,825 22 11 0 0

22 71,899 22 688 34 0

23 95,774 22.1 718 11 0

24 86,927 21.9 853 0 0

25 77,373 21.9 1,067 0 0

26 74,649 22.2 187 53 0

27 53,456 22.1 210 16 0

Mean temperature 21.8

Total area of the

27 sectors

1,477,860

Total area 1–3°C 

below mean temperature 

(percentage of total 

27-kilometer reach)

6,460 (0.44) 211 (0.014) 0 (0)
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 31

Table 12. Median temperature for each 1-kilometer section and refuge areas 1, 2, and 3oC below the median temperature for 

that section, during three flights along the 27-kilometer reach of the Indian and Hudson Rivers from the outflow point of the 

Abanakee Dam to North Creek, Adirondack Mountains, New York, July 25, 2005.—Continued

[Flight 1 aloft from 10:12 to 10:55 EDT; flight 2 aloft from 12:39 to 13:14 EST; flight 3 aloft from 15:42 to 16:05 EDT. Sections of the river under the 

high-water bubble are highlighted. Locations of study sites are shown in figure 1; unit conversions are shown in the conversion tables at the front of the 

report. Site codes are listed in table 1. oC, degrees Celsius]

Flight 3

Section

(kilometers from 

outflow point)

Total area

(square meters)

Median 

temperature

(°C)

Refuge area below median temperature (square meters)

1oC 2oC 3oC

1 18,765 23.2 1,268 421 23

2 22,327 23.4 1,569 33 0

3 44,228 23.5 2,252 137 3

4 25,025 24.2 2,509 174 0

5 50,741 23.9 703 94 0

6 60,772 23.8 721 42 0

7 57,199 23.2 218 43 0

8 56,271 23.1 1,017 53 7

9 60,937 23 916 85 1

10 51,812 23 300 0 0

11 43,487 22.9 705 150 2

12 49,484 22.8 740 11 0

13 44,654 23.1 137 0 0

14 48,162 23.1 287 29 0

15 58,047 22.5 250 0 0

16 5,507 22.4 0 0 0

17 56,718 22.2 0 0 0

18 62,784 22 9 0 0

19 69,463 22.1 16 0 0

20 76,905 22.3 1 0 0

21 63,684 22.4 0 0 0

22 71,676 22.6 0 0 0

23 94,986 22.9 0 0 0

24 86,544 23.1 136 0 0

25 77,104 23.5 6 0 0

26 74,531 23.9 11 0 0

27 53,405 23.9 21 0 0

Mean temperature 23.1

Total area of the

27 sections

1,485,218

Total area 1–3°C 

below mean temperature 

(percentage of total 

27-kilometer reach)

13,792 (0.92) 1,272 (0.09) 36 (0.002)
32 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

shaded some of the exposed rocks on the east bank and made 

them appear much cooler than the surrounding rocks and 

water; this created two potential problems. First, the shade 

made the rocks appear as though they were providing a 

thermal (wet) refuge, which disappeared once the shade was 

gone and the rocks warmed. Second, it biased or lowered all 

estimates of mean and median temperatures for the affected 

1-km sections. This situation made delineations of actual 

refuges (which are defined relative to water temperature 

within the section) less accurate. To minimize this problem, 

each 1-km river section was divided in half along the thalweg, 

and then temperature data only for the half-section with the 

lesser amount of unshaded bank (that had been shaded in the 

morning) was summarized. This analysis produced results 

similar to those from the analysis of whole 1-km sections 

for the second and third flights but very different from the 

initial results for the first flight. During the first flight, only 

0.7 percent (5,092 m2) of unshaded water surface was 1 to 

3oC cooler than the median (table 13), whereas 4.1 percent 

of surface water reached those temperatures in the wholeriver analysis (table 12). These contrasting results indicate 

that much of the area characterized initially as refuge in 

shaded half-sections may have actually been exposed rocks. 

During the second and third flights, the percentages of 

potential refuges based on either half or whole sections were 

comparable. Most river sections included little refuge area 

during the midday flight. During the afternoon flight, the lower 

half of the river provided little potential thermal refuge; the 

decrease in available refuge area became measureable 5 km 

upstream from the high-water bubble and continued through 

the end of the reach (table 13).

Five tributaries entering the river had localized cooling 

effects on river-water temperatures; all of these tributaries are 

in the lower third of the study reach at or below the confluence 

of the Hudson River and the Boreas River (fig. 15). The effects 

of cold-water tributaries on river temperatures are denoted by 

hand-drawn areas in figure 16. Cold tributary waters fill 15 

to 25 percent of the hand-delineated area at low flow within 

each of these areas and provide most of the near-bank and 

off-channel thermal refuges in the study reach. The Boreas 

River at kilometer 19 and Deer Creek at kilometer 27 enter 

the Hudson River on its east bank (fig. 15); therefore, these 

tributaries appeared to provide more refuge for trout during 

the morning flight (table 14), probably because of spurious 

shading. The other three tributaries (Raquette Brook at 

kilometer 24, Aldous Brook at kilometer 25, and Thirteenth 

Lake Outlet at kilometer 26) enter the Hudson River on its 

west bank and provided more potential thermal refuge during 

the midday flight than during the morning flight (table 14). 

The Boreas tributary was warmer than the Hudson River 

at their confluence during the afternoon flights; the other 

four tributaries were cooler than the Hudson River at their 

confluence during the afternoon flights, but their effect on 

Hudson River temperatures was negligible (table 14, fig. 16).

River Habitat 

River habitat was characterized by surveys of GCUs 

under base flow throughout the lower Indian River and at 

the four study reaches in the Hudson River. The effects of 

the releases on habitat were quantified by changes in the 

distribution of GCUs during high flows at seven sampled 

reaches in both rivers (fig. 2). Data from sampled reaches 

were compared to data from the same areas at base flow, even 

though the total lengths mapped at base flow and at high flow 

differed because GCUs did not always start and end in the 

same location under different flow regimes (for example, at 

HR02 and HR03). Runs and rapids were the dominant or sole 

GCUs at high (release) flows; however, although runs and 

riffles dominated the upstream portion of the Indian River 

during base flow, only riffles dominated the downstream 

portion (table 15). GCU composition of the Indian River 

during base flow changed at the river’s confluence with the 

Hudson River. Riffles were still common, but glides and 

other fast-water GCUs (riffle, run, or rapids) dominated 

habitat during base flow at all four reaches of the Hudson 

River. Except for the Hudson River Gorge, most reaches of 

the Hudson River were wider and less steep than those in the 

Indian River, which probably allowed more slow-water habitat 

(glides) to dominate. Runs and rapids were the dominant 

GCUs along the Hudson River at high flows; glides were also 

a dominant GCU at the farthest downstream site (HR05). 

Slow-water habitats (pool, glide, backwater, side 

channel) decreased from 31 percent during base flow to 

7 percent during high (release) flow in the Indian River, from 

45 percent during base flow to 21 percent during high flow 

in the Hudson River, and from 41 percent during base flow 

to 16 percent during high flow overall. Fast-water habitats 

(riffle, run, rapids) increased from 69 percent during base flow 

to 93 percent during release flow in the Indian River, from 

55 percent during base flow to 79 percent during high flow 

in the Hudson River, and from 59 percent during base flow 

to 84 percent during high flow overall. Fewer GCUs were 

present during high flows than during base flows in all study 

reaches (table 15). Except for HR02 and HR03, where habitat 

surveys were shortened during high flows, total habitat areas 

of all study reaches were generally similar during base flow 

and high flow because both areas were mapped onto the same 

aerial photograph. Since the photograph was taken at low flow, 

it did not account for changes in stream width associated with 

high flow. 

Distribution of Wetlands 

Wetlands accounted for approximately 18 percent of the 

area along river banks in the Indian River, 25 percent near 

study reaches in the upper Cedar River, and 46 percent in the 

lower Cedar River (fig. 3, table 16). The average widths of 
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 33

Table 13. Median temperature and refuge areas 1, 2, and 3°C below the median temperature for unshaded halves of each 

1-kilometer section divided along the thalweg along the 27-kilometer reach of the Indian and Hudson Rivers from the outflow point of 

the Abanakee Dam to North Creek, Adirondack Mountains, New York. 

[Halves are for the downstream view of each section. Sections under the high-water bubble are highlighted. Flight 1 aloft from 10:12 to 10:55 EST; flight 2 

aloft from 12:39 to 13:13 EST; flight 3 aloft from 15:42 to 16:05 EST. Locations of study sites are shown in figure 1; unit conversions are shown in the 

conversion tables at the front of the report. Site codes are listed in table 1. oC, degrees Celsius]

Flight 1

Section

(kilometers from 

outflow point)

Half Total area

(square meters)

Median 

temperature

(°C)

Refuge area below median temperature (square meters)

1oC 2oC 3oC

1 L 11,934 20.8 248 14 0

2 L 9,887 20 131 0 0

3 L 23,667 20.2 244 10 0

4 L 13,792 20.7 463 44 0

5 L 28,529 20.6 14 0 0

6 L 32,569 20.1 1 0 0

7 L 28,712 19.8 119 0 0

8 L 30,894 19.7 486 0 0

9 L 31,442 20 120 0 0

10 R 21,119 19.7 33 0 0

11 L 22,862 19.5 438 18 0

12 L 27,184 19.5 354 49 0

13 L 26,171 19.8 0 0 0

14 L 26,240 19.7 19 0 0

15 L 30,665 19.7 7 0 0

16 L 3,639 20.2 0 0 0

17 L 29,646 20.2 57 0 0

18 L 31,845 20 0 0 0

19 L 37,823 19.9 1,408 323 0

20 R 41,926 19.9 47 0 0

21 R 28,239 20 412 73 0

22 R 38,289 20 216 0 0

23 R 45,181 19.6 0 0 0

24 R 36,945 19.4 0 0 0

25 R 37,112 17.7 1 0 0

26 R 34,561 19.4 274 26 0

27 R 27,838 19.2 0 0 0

Mean temperature 19.9

Total area of the

27 sections

758,711

Total area 1–3°C 

below mean 

temperature 

(percentage of total 

27-kilometer reach)

5,092 (0.7) 557 (0.1) 0 (0) 
34 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

Table 13. Median temperature and refuge areas 1, 2, and 3°C below the median temperature for unshaded halves of each 

1-kilometer section divided along the thalweg along the 27-kilometer reach of the Indian and Hudson Rivers from the outflow point of 

the Abanakee Dam to North Creek, Adirondack Mountains, New York.—Continued

[Halves are for the downstream view of each section. Sections under the high-water bubble are highlighted. Flight 1 aloft from 10:12 to 10:55 EST; flight 2 

aloft from 12:39 to 13:13 EST; flight 3 aloft from 15:42 to 16:05 EST. Locations of study sites are shown in figure 1; unit conversions are shown in the 

conversion tables at the front of the report. Site codes are listed in table 1. oC, degrees Celsius]

Flight 2

Section

(kilometers from 

outflow point)

Total area

(square meters)

Median 

temperature

(°C)

Refuge area below median temperature (square meters)

1oC 2oC 3oC

1 12,244 22.3 20 0 0

2 10,143 22.1 2 0 0

3 23,947 21.9 4 0 0

4 13,971 22.1 2 0 0

5 28,649 21.9 0 0 0

6 32,567 22 1 0 0

7 28,785 21.8 0 0 0

8 31,025 21.9 6 0 0

9 31,414 21.7 3 0 0

10 21,556 21.4 0 0 0

11 22,833 21 0 0 0

12 27,170 20.9 1 0 0

13 26,149 21.2 0 0 0

14 16,614 21.3 364 0 0

15 30,755 21.3 2 0 0

16 3,676 21.5 0 0 0

17 29,613 22.2 1,949 0 0

18 31,772 21.8 6 0 0

19 37,778 21.9 301 0 0

20 42,312 22 7 0 0

21 28,590 22.1 8 0 0

22 38,624 22.2 52 0 0

23 45,660 22.3 1 0 0

24 37,407 22 10 0 0

25 37,590 22.1 0 0 0

26 34,898 22.4 173 66 0

27 28,087 22.2 1 0 0

Mean temperature 21.9

Total area of the 

27 sections

753,829

Total area 1–3°C 

below mean temperature 

(percentage of total 

27-kilometer reach)

2,913 (0.4) 66 (0) 0 (0)
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 35

Table 13. Median temperature and refuge areas 1, 2, and 3°C below the median temperature for unshaded halves of each 

1-kilometer section divided along the thalweg along the 27-kilometer reach of the Indian and Hudson Rivers from the outflow point of 

the Abanakee Dam to North Creek, Adirondack Mountains, New York.—Continued

[Halves are for the downstream view of each section. Sections under the high-water bubble are highlighted. Flight 1 aloft from 10:12 to 10:55 EST; flight 2 

aloft from 12:39 to 13:13 EST; flight 3 aloft from 15:42 to 16:05 EST. Locations of study sites are shown in figure 1; unit conversions are shown in the 

conversion tables at the front of the report. Site codes are listed in table 1. oC, degrees Celsius]

Flight 3

Section

(kilometers from 

outflow point)

Total area

(square meters)

Median 

temperature

(°C)

Refuge area below median temperature (square meters)

1oC 2oC 3oC

1 9,276 23.2 854 320 23

2 10,143 23.2 598 2 0

3 23,795 23.5 2,145 137 3

4 13,971 24.1 2,053 105 0

5 28,649 24 83 0 0

6 32,567 24.1 82 2 0

7 28,785 23.4 71 0 0

8 26,141 23.1 903 49 5

9 31,414 23.2 157 16 0

10 21,556 22.8 91 0 0

11 22,833 23.1 1 0 0

12 27,170 22.9 0 0 0

13 26,149 23.2 0 0 0

14 26,644 23.1 0 0 0

15 30,755 22.4 72 0 0

16 3,676 22.4 0 0 0

17 29,629 22.4 0 0 0

18 31,772 22.1 0 0 0

19 37,778 22.2 4 0 0

20 42,312 22.2 0 0 0

21 28,590 22.3 0 0 0

22 38,624 22.6 0 0 0

23 45,540 22.9 0 0 0

24 37,333 23.2 0 0 0

25 37,590 23.5 0 0 0

26 34,898 23.9 0 0 0

27 28,087 24 20 0 0

Mean temperature 23.1

Total area of the 

27 sections

755,677

Total area 1–3°C 

below mean temperature 

(percentage of total 

27-kilometer reach)

7,134 (0.9) 631 (0.1) 31 (0) 
36 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

28N

74°24' 74°12' 74°

43°48'

43°42'

28

28

30

Base from U.S. Geological Survey Digital Data.

Universal Transverse Mercator Projection, Zone 18N, NAD83

WARREN COUNTY

Wakely

Dam

Indian Lake

North River

Cedar River

Dam

Boreas River

Indian River

Hudson River

Indian Lake

HAMILTON COUNTY

ESSEX COUNTY

Cedar River 

Flow

Lake Abanakee

Cedar River

Hudson River

Abanakee

Dam

Browns Brook

Map Area

NEW YORK

Adirondack

Park

78° 76° 74°

42°

44°

Warrensburg

CR04

CR03

CR02

CR01

HR05

HR04

HR03

HR02

HR01

IR03

IR02

IR01

0 3 6 KILOMETERS

0 3 6 MILES

Deer C reek

Raquet te Brook

Aldous Broo k

Thirteenth Brook

Ba ml ofGilead

Brook

Brook

Griffin

Thirteenth Lake

Brook

B ear

Trap

EXPLANATION

Village and name

Study site and identifier

Confluence of cool-water tributary

Hudson gorge primitive area

HR01

North River

Figure 15. Map showing fFive tributaries entering the bottom third of the study reach at or below the confluence of the 

Hudson River with the Boreas River, Adirondack Mountains, New York. Study-site codes are listed in table 1.

wetlands were similar along both the Indian River and lower 

Cedar River. Wetland widths could not be measured in the 

upper Cedar River because access was restricted.

Fish Communities

Fish surveys were conducted at least once at four 

control sites in the Cedar River, three affected sites in the 

Indian River, one control site in the Hudson River, and three 

affected sites in the Hudson River during 2005 and 2006. 

Fish-community indexes and the density and biomass of 

individual fish populations were evaluated to test hypotheses 

that fish communities at the three Indian River sites (IR01, 

IR02, and IR03) were negatively affected by the releases, 

and fish communities at the three downstream sites on 

the Hudson River (H02, H04, and H05) were negatively 

affected by the releases. Because the Cedar River contains a 

run-of-the-river impoundment (Wakely Dam), comparison 

of fish indexes for Cedar River sites with those for Indian 

River sites was expected to illustrate the relative effects of 

frequent releases on biota in the Indian River. Comparison of 

community indexes for the three downstream Hudson River 

sites (HR02, HR04, and HR05) with indexes for the upstream 

control site (HR01) and with each other allows identification 

of the significant effects, possibly diminishing downstream, 

associated with releases. If releases are assumed to have only 

nominal effects on fish communities in the Hudson River, then 

comparison of community indexes from Hudson River and 

Indian River sites would be expected to reveal the combined 

effects of the impoundment and releases on fish communities 

at the three Indian River sites.

Community Indexes—The effects of releases on total 

density and biomass of fish communities differed among 

sites in the Indian River and the Hudson River, as expected. 

Total community density and biomass at the Indian River 

site immediately downstream from the dam (IR01) were on 
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 37

Table 14. Median temperature and refuge areas .5, 1, 1.5, and 2°C below the median temperature for each 1-kilometer section 

along the 27-kilometer reach of the Indian and Hudson Rivers from the outflow point of the Abanakee Dam to North Creek, 

Adirondack Mountains, New York, 2005.

[Flight 1 aloft from 10:12 to 10:55 EST; Flight 2 aloft from 12:39 to 13:13 EST; Flight 3 aloft from 15:42 to 16:05 EST. Sections under the high-water 

bubble are highlighted Locations of study sites are shown in figure 1; unit conversions are shown in the conversion tables at the front of the report. Site 

codes are listed in table 1°C, degrees Celsius]

Section

(kilometer from 

outflow point)

Tributary

Total

area

(square 

meters)

Median

temperature

(°C)

Refuge area below median temperature (square meters)

0.5°C 1.0°C 1.5°C 2.0°C

Flight 1

19 Boreas River 6,026 19.6 1,901 1,347 582 90

24 Raquette Brook 1,911 19.5 75 2 0 0

25 Aldous Brook 1,351 19.9 22 9 0 0

26 Thirteenth Lake Outlet 5,397 19.4 578 402 252 63

27 Deer Creek 2,590 18.8 554 362 139 14

Flight 2

19 Boreas River 6,026 21.9 977 296 11 0

24 Raquette Brook 1,911 22.3 256 93 22 8

25 Aldous Brook 1,351 22.3 977 296 11 0

26 Thirteenth Lake Outlet 5,397 22.4 707 281 212 136

27 Deer Creek 2,590 22.1 348 205 74 16

Flight 3—passage of bubble

19 Boreas River 6,026 22.4 9 0 0 0

24 Raquette Brook 1,911 23.4 84 47 15 0

25 Aldous Brook 1,351 23.5 35 0 0 0

26 Thirteenth Lake Outlet 5,397 24 13 0 0 0

27 Deer Creek 2,590 23.8 1 0 0 0

average between 10 and 45 percent of density and biomass 

estimates for other sites on the Indian River (table 17), and 

they were significantly lower than estimates for all other sites 

except HR04 in the three rivers (fig. 17). The differences 

between estimates of density and biomass at the next two 

downstream sites on the Indian River (IR02 and IR03) and 

at the two downstream sites on the Cedar River (CR03 and 

CR04, downstream from Wakely Dam) were generally minor. 

Density and biomass at IR02 and IR03, however, were similar 

to or somewhat higher than at most sites on the Hudson River. 

They were also similar to density and biomass estimates for 

most Cedar River sites, excluding CR02 (fig. 17). Except for 

IR01, community density and biomass at Indian River sites 

were comparable to the same indexes for most Cedar River 

and Hudson River sites. Total community density and biomass 

at the Hudson River sites downstream from its confluence 

with the Indian River (HR02, HR04, and HR05) were neither 

consistently lower nor higher than the same indexes at the 

control site (HR01) (table 17, fig. 17). Elevated (storm) flows 

during fish surveys may have affected sampling efficiencies 

at HR04, but the releases did not adversely affect total 

community biomass and density at most Hudson River sites. 

The significant difference between estimates of biomass and 

density at IR01 and at CR01 and the decrease in estimates 

of biomass and density at HR02 indicate that the releases 

slightly affected fish communities at IR01 and HR02. Many 

other physical, chemical, and biological factors would need 

to be quantified, however, to determine whether observed 

differences were caused solely by releases or by some 

combination of releases and related factors.
38 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

A 10:12 Eastern Standard Time

B 12:39 Eastern Standard Time

C 15:42 Eastern Standard Time

EXPLANATION

Surface temperature 3 degrees above the mean

Surface temperature equal to the mean

Surface temperature 3 degrees below the mean

Raquette Brook

Deer Creek

0

0

50 METERS

100 200 FEET

Figure 16. False-color images of the confluences of Raquette Brook at kilometer 

24 and Deer Creek at kilometer 27 with the Hudson River during flights at A,10:12,

B, 12:39, and C, 15:42 Eastern Standard Time in the Adirondack Mountains, New 

York. The release slug passed these tributaries during the third flight, reducing any 

cold-water effect.
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 39

Table 15. Areal percentage of seven types of 

geomorphic channel units (GCUs) in the Indian River, 

Adirondack Mountains, New York, at base and high flow 

on August 4, 17, and 18, 2005, and the total area and 

number of GCUs mapped.—Continued

[Locations of study sites are shown in figure 1; unit conversions are 

shown in the conversion tables at the front of the report. Site codes 

are listed in table 1.]

GCU type Base flow High flow

IR01

Percentage of GCU area mapped

Rapid 9.5 28.7

Riffle 21.5 1.3

Run 36.2 56.6

Glide 5.7 0

Pool 13.7 0

Backwater 6.1 6.7

Side channel 7.3 6.7

Number of GCUs

24 17

Total area, in square meters

42,262 42,198

IR03

Percentage of GCU area mapped

Rapid 5.6 32.8

Riffle 62.4 0

Run 2.2 67.2

Glide 14.5 0

Pool 0 0

Backwater 15.3 0

Side channel 0 0

Number of GCUs

10 6

Total area, in square meters

40,271 34,820

Table 15. Areal percentage of seven types of 

geomorphic channel units (GCUs) in the Indian River, 

Adirondack Mountains, New York, at base and high flow 

on August 4, 17, and 18, 2005, and the total area and 

number of GCUs mapped.—Continued

[Locations of study sites are shown in figure 1; unit conversions are 

shown in the conversion tables at the front of the report. Site codes 

are listed in table 1.]

GCU type Base flow High flow

HR02

Percentage of GCU area mapped

Rapid 3.9 0

Riffle 35.0 0

Run 9.4 94.7

Glide 47.5 0

Pool 0 0

Backwater 4.3 5.3

Side channel 0 0

Number of GCUs

14 5

Total area, in square meters

69,230 25,039

HR03

Percentage of GCU area mapped

Rapid 48.4 46.3

Riffle 0 0

Run 7.7 28.6

Glide 29.6 0

Pool 14.3 25.0

Backwater 0 0

Side channel 0 0

Number of GCUs

6 5

Total area, in square meters

64,512 35,435
40 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

Though statistical analyses were not feasible with other 

standard indexes of community health (for example, richness, 

diversity, equitability, and dominance) at individual sites, 

several differences were apparent among sites in both affected 

rivers (and in the Cedar River) or when data from each site 

were pooled by river. Community richness (number of fish 

species) was consistently one to seven species lower at all 

Indian River sites than at all other study sites (table 17, fig. 18) 

and three to six species lower than at the two downstream 

sites on the Cedar River. Richness at HR01 was similar to 

that at HR02 and at HR04 but was four species lower than at 

HR05. Overall, mean richness at the three Indian River sites 

was significantly lower (p < 0.05) than at the four Hudson 

River sites or at the four Cedar River sites. Owing to high 

variability in most other indexes among study sites, no other 

indexes differed significantly among the three river systems. 

Species diversity and equitability values for IR01, IR02, and 

IR03 varied slightly, but on average they were similar to the 

same indexes at CR01, CR02, CR03, and CR04. Estimates of 

species diversity and equitability at CR03 and CR04 averaged 

almost twice as high as the same indexes at IR02 and IR03. 

These results indicate that fish communities at the Indian 

River sites functioned differently, and that their structure was 

less balanced than at communities at the Cedar River control 

sites. Community equitability was low and dominance was 

high immediately downstream from the Wakely Dam (CR01); 

both indexes also appeared to be affected at CR02 (compared 

to CR03 and CR04). No large predator species were present, 

and one or two minnow species dominated communities at 

CR01and CR02. Species richness, diversity, and equitability 

were generally higher, and dominance was lower, at the three 

Hudson River sites downstream from the confluence with 

the Indian River (HR02, HR04, and HR05) than at HR01, 

indicating that the function of fish communities at affected 

Hudson River sites was slightly different from, but more 

balanced than, the community at the control site (HR01).

Opposing downstream trends at affected sites in the 

Hudson and Indian Rivers indicate that either normal 

variability in fish indexes is high (and real effects cannot be 

quantified) or that there are negative effects when relative 

changes in flow are large and positive effects when relative 

changes in flow are small or moderate. The intermediatedisturbance theory may account for different community 

responses; it indicates that the most diverse communities 

develop in areas with intermediate levels of disturbance 

(Ward and Stanford, 1983; Death and Winterbourn, 1995; 

McCabe and Gotelli, 2000). Although reduced species 

richness, diversity, and equitability indicate that the integrity 

of fish communities at all Indian River sites may be adversely 

affected by releases, it is currently impossible to prove that 

other factors do not also contribute to observed differences 

among sites. Additional (replicated) fish-community data, 

hydrologic data, and more detailed habitat information would 

allow full characterization of site-to-site similarities and 

differences and a more complete assessment of the potential 

effects of the releases.

Table 15. Areal percentage of seven types of 

geomorphic channel units (GCUs) in the Indian River, 

Adirondack Mountains, New York, at base and high flow 

on August 4, 17, and 18, 2005, and the total area and 

number of GCUs mapped.—Continued

[Locations of study sites are shown in figure 1; unit conversions are 

shown in the conversion tables at the front of the report. Site codes 

are listed in table 1.]

GCU type Base flow High flow

HR04

Percentage of GCU area mapped

Rapid 0 23.4

Riffle 41.3 25.4

Run 15.0 33.5

Glide 27.9 17.6

Pool 14.8 0

Backwater 1.0 0

Side channel 0 0

Number of GCUs

12 6

Total area, in square meters

 81,488 93,146

HR05

Percentage of GCU area mapped

Rapid 11.4 8.7

Riffle 8.2 20.4

Run 38.3 35.3

Glide 37.2 32.9

Pool 0 0

Backwater 2.9 0.4

Side channel 2.0 2.3

Number of GCUs

12 8

Total area, in square meters

143,473 152,441
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 41

Table 16. Lengths and areas of wetlands along the Indian River and along surveyed sections of the upper and lower 

Cedar River, Adirondack Mountains, New York, 2005, and the percentages of river length bordered by wetlands. 

[Length of wetlands includes banks and any islands having wetlands. Length of river includes length of islands, if any, (in parentheses); unit 

conversions are shown in the conversion tables at the front of the report. --, no data available]

River

Area 

of wetlands 

(square meters)

Length 

of wetlands 

(meters) 

Percentage 

of river length 

bordered 

by wetlands

Length 

of river 

surveyed 

(kilometers) 

Indian River 4,557 1,576 18 4.37

Upper Cedar River -- 219 25 0.62 (0.27)

Lower Cedar River 1,172 375 46 0.69 (0.13)

Table 17. Estimates of fish-community parameters for 11 study sites on the Indian, Hudson, and Cedar Rivers, 

Adirondack Mountains, New York, 2005 and 2006.

[Equitability was measured as Shannon-Weiner H′, dominance as Simpson's C, and diversity as the number of species divided by the 

number of individuals in the sample. Locations of study sites are shown in figure 1; unit conversions are shown in the conversion tables at 

the front of the report. Study-site codes are listed in table 1. m2, square meters; ha, hectare; g, grams]

Study 

sites

Parameter

Sample area 

(square 

meter)

Richness 

(number of 

species)

Density 

(number 

of fish 

per 0.1 ha)

Biomass 

(g per 0.1 ha) Diversity Equitability Dominance

CR01 305 6 1,382 1,542 2.34 0.35 0.58

CR02 432 7 2,265 3,489 2.35 0.51 0.38

CR03 468 8 276 1,758 3.82 0.71 0.25

CR04 427 10 234 1,264 5.08 0.83 0.20

IR01 803 5 24 560 3.91 0.66 0.24

IR02 237 5 241 1,594 2.85 0.54 0.34

IR03 252 4 159 1,244 2.50 0.48 0.40

HR01 352 7 233 1,159 3.68 0.51 0.47

HR02 311 6 112 770 3.89 0.61 0.30

HR04 197 7 168 226 4.61 0.67 0.27

HR05 378 11 872 1,282 4.38 0.76 0.21
42 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

0

1,000

2,000

3,000

4,000

CR01 CR02 CR03 CR04 IR01 IR02 IR03 HR01 HR02 HR04 HR05

FISH-CO

M

M

U

NIT

Y DENSIT

Y,

IN

N

U

MBER PER 0.1 HECT

ARE

CO

M

M

U

NIT

Y BIO

M

ASS,

IN

GRA

MS PER 0.1 HECT

ARE

Density

Biomass

0

1,000

2,000

3,000

4,000

STUDY-SITE CODE

95-percent confidence interval

Figure 17. Graph showing eEstimates of density, biomass, and 95-percent confidence intervals for 

fish communities surveyed at 11 study sites on the Cedar, Indian, and Hudson Rivers, Adirondack 

Mountains, New York, 2005–06. Locations of study sites are shown in figure 1; study-site codes are 

listed in table 1.

0.1

1.0

10.0

100.0

CR01 CR02 CR03 CR04 IR01 IR02 IR03 HR01 HR02 HR04 HR05

FISH-COMMUNITY INDEX

STUDY-SITE CODE

Diversity

Equitability

Richness

Dominance

Figure 18. Graph showing dDiversity, equitability, richness, and dominance for fish 

communities at 11 study sites in the Cedar, Indian, and Hudson Rivers, Adirondack 

Mountains, New York, 2005–06. Locations of study sites are shown in figure 1; studysite codes are listed in table 1.
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 43

The general upward trend in several community indexes 

at Indian River sites (with increasing drainage area) tends 

to support the river-continuum concept (Montgomery, 

1999; Power and others, 1999; Walters and others, 2003). 

Community richness, equitability, and diversity consistently 

increase, and dominance decreases, in the Cedar and the 

Hudson Rivers as fish communities acquire more species and 

become more diverse, complex, and balanced at downstream 

sites where drainage areas increase, and river reaches become 

more interconnected, warmer, larger, and generally more 

productive (Montgomery, 1999; Power and others, 1999; 

Walters and others, 2003; Robinson and Rand, 2005). Trends 

in these four indexes are clearly reversed between sites 

IR01 and IR03 in the Indian River (fig. 18). These unusual 

trends suggest either that site conditions may essentially be 

equivalent (for example, size and community health), so that 

the normal variability identifies false differences in indexes, 

or normal processes within and interactions among different 

levels of ecological organization (species assemblages) may 

have truly been disrupted. The similarity of the drainage areas 

of the three Indian River study sites (505 to 518 km2) indicates 

that the first option is plausible. Additional evidence from 

the benthic macroinvertebrate communities may be useful in 

determining whether there is an alternative reason (other than 

the releases) for the trends noted in fish communities of the 

Indian River.

Density of Fish Populations—The density (and biomass) 

of individual species populations (table 18) show how fish 

communities and related indexes differ among sites and 

help qualify the effects of releases on fish communities. A 

few rock bass and rainbow trout and a small population of 

redbreast sunfish were most abundant and dominated the fish 

community at IR01. Dominant species differed at the Cedar 

River site immediately downstream from the unregulated 

Wakely Dam (CR01), where blacknose dace, common shiner, 

and white sucker were most abundant (table 18, fig. 19). Slimy 

sculpin, longnose dace, cutlips minnow, and smallmouth bass 

were most abundant and dominated communities at the other 

two Indian River sites (IR02 and IR03). Fallfish and many of 

the same species found at IR02 and IR03 dominated the fish 

community at HR02. The overall effect of the releases on fish 

communities in the Indian River appears to be caused by an 

actual loss of fish species rather than by species replacements 

or by small decreases in the numbers of endemic species. For 

example, 15 or 16 species, including blacknose dace, common 

shiner, creek chub, bluntnose minnow, central mudminnow, 

margined madtom, and white sucker were collected at Cedar 

River sites, whereas none of these species were found in the 

Indian River (table 18). Slimy sculpin also were present in the 

Indian River but not at any Cedar River site. Fish communities 

at the two upstream Cedar River sites (CR01 and CR02) were 

different from those at the downstream Cedar River sites 

(CR03 and CR04), possibly because no large piscivorous 

species (predators such as largemouth or smallmouth bass) 

were observed at the two upstream sites. The two upstream 

sites were situated between the Cedar River Dam and the 

Wakely Dam (fig. 1), which may have blocked both bass 

species from the intervening reach of the Cedar River. 

Populations of brook trout and brown trout have also been 

observed in the same river section, but their densities are low, 

and they appear to concentrate at river margins and in cooler 

tributaries during the warmer months.

The effects of the releases on fish communities of the 

Hudson River were less obvious than or contrary to the effects 

of releases observed in the Indian River. As with the Indian 

River sites, we did not collect common shiner and creek 

chub at the first potentially affected site on the Hudson River 

(HR02) or at the control site (HR01); however, both species 

were collected from sites farther downstream (table 18). 

Although four species (central mudminnow, stonecat, 

redbreast sunfish, and rock bass) were unique to the control 

site, eight more species (common shiner, creek chub, longnose 

dace, slimy sculpin, margined madtom, largemouth bass, 

brown trout, and rainbow trout) were observed at potentially 

affected sites but not at the control site (HR01) (table 18, 

fig. 19). Trout were collected only from sites where NYSDEC 

stocked 1- or 2-year-old trout (HR05 and IR01). In general, 

the releases appear to cause small changes in the densities of 

some fish species at several Hudson River sites, replacement 

of a few species at HR02 and HR04 (rather than potential 

loss of species as noted in the Indian River), and little or no 

adverse effect on fish populations at HR05. The overall effects 

of the releases on densities of fish communities in the Hudson 

River appeared to be nominal. Any effect of the releases on 

communities at HR05, however, would appear to be positive 

because community density, as well as biomass, richness, 

diversity, and equitability, were as high, or higher than, levels 

found at all other study sites in the Hudson River.

Biomass of Fish Populations—Biomass may be a better 

gage (of the effects of releases on fish communities) than 

density because biomass tends to fluctuate less widely than 

density (it is more conservative) when fish react to biotic, 

habitat, and water-quality stresses (Baldigo and Lawrence, 

2001). Biomass data for species populations in this study 

were, in fact, much less variable among sites (total biomass 

varied 16-fold) than density (total density varied 103-fold) 

(tables 18, 19). Although biomass of rock bass, redbreast 

sunfish, and rainbow trout dominated the fish community 

at IR01 (like density), total biomass was about one-third of 

that estimated at CR01, where blacknose dace dominated the 

community (table 19, fig. 20). The biomass of slimy sculpin, 

cutlips minnow, rock bass, and smallmouth bass dominated 

fish communities at the other two Indian River sites (IR02 

and IR03); except for sculpin, the same species dominated 

communities at the two upstream Hudson River sites (HR01 

and HR02). The total biomass of fish communities at CR02 

consisted mostly of blacknose dace and common shiner and 

was more than twice as large as the total biomass at CR01 

(table 19, fig. 20). The biomass of cutlips minnows and 

either margined madtom or rock bass dominated the fish 

communities at both downstream Cedar River sites (CR03 

and CR04) (fig. 20). The biomass of cutlips minnow, longnose 
44 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06 Table 18. Estimates of density for each fish species collected at each of 11 study sites on the Indian, Hudson, and Cedar Rivers, Adirondack Mountains, New York, 2005–2006. [Densities measured in number of fish per 0.1 hectare. Locations of study sites are shown in figure 1; unit conversions are shown in the conversion tables at the front of the report. Study-site codes are listed in table 1.] Common name Study sites CR01 CR02 CR03 CR04 IR01 IR02 IR03 HR01 HR02 HR04 HR05 Creek chub 7 167 9 5 0 0 0 0 0 20 0 Common shiner 233 914 47 112 0 0 0 0 0 0 238 Stonecat 0 0 0 0 0 0 0 6 0 0 0 Bluntnose minnow 0 37 0 21 0 0 0 0 0 0 0 Central mudminnow 0 0 0 7 0 0 0 14 0 0 0 Fallfish 0 0 0 0 0 0 0 150 48 71 206 Redbreast sunfish 0 0 0 9 6 0 0 3 0 0 0 White sucker 108 32 0 0 0 0 0 0 0 0 8 Cutlips minnow 0 0 58 87 0 110 20 14 6 25 190 Margined madtom 0 0 111 5 0 0 0 0 10 5 21 Brown bullhead 3 0 0 0 0 0 0 0 0 0 0 Brown trout 0 0 0 0 0 0 0 0 0 0 3 Rainbow trout 0 0 0 0 2 0 0 0 0 0 3 Northern redbelly dace 0 2 0 0 0 0 0 0 0 0 0 Blacknose dace 1,034 1,027 17 0 0 0 0 0 0 0 0 Longnose dace 0 79 19 16 0 84 91 0 10 5 137 Largemouth bass 0 0 0 0 7 0 0 0 3 0 0 Smallmouth bass 0 0 6 9 2 21 36 31 35 36 13 Rock bass 0 0 4 28 5 13 0 9 0 0 0 Slimy sculpin 0 0 0 0 0 13 12 0 0 0 11 Other minnows 3 0 0 0 0 0 0 0 0 5 42 Total 1,388 2,258 271 299 22 241 159 227 112 167 872
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 45

dace, smallmouth bass, and rock bass populations at CR04, 

IR02, IR03, and possibly at HR01 were relatively well 

balanced and generally alike, but the species (and biomass 

of each) differed from those at sites farther upstream in 

the Cedar River (table 19, fig. 20). The biomass of cutlips 

minnow, rock bass, smallmouth bass, or some combination of 

these three species dominated the total community biomass at 

CR04, IR02, IR03, and HR01. Differences between species 

and biomass at Indian River sites IR02 and IR03 and at 

Cedar River sites CR01 and CR02 could be related to the 

absence of predator species at the upstream Cedar River sites 

(as discussed earlier) or to the divergence in environmental 

conditions at the lower Indian River sites. Sites IR02 and 

IR03 have drainage areas of 513 to 518 km2, and Cedar 

River sites have drainage areas that decrease from 425 km2

at CR04 to 213 km2 at CR03 to 149 km2 at CR02 and to 117 

km2 at CR01. The biomasses of rainbow trout populations at 

IR01 and HR05 were relatively high (table 19, fig. 20) but 

much lower than would be expected shortly after springtime 

stocking. These findings suggest that, although community 

structure (species richness and densities of some species 

populations) was strongly affected at all three Indian River 

sites, community function (total biomass, and the biomasses 

and densities of dominant species populations) was severely 

affected by releases at only the first site downstream from 

Lake Abanakee (IR01).

The biomasses of species populations at most Hudson 

River study sites show no consistent trends that could be 

attributed to flow releases. Three to six species, including 

common shiner, cutlips minnow, fallfish, white sucker, 

smallmouth bass, and trout dominated the biomasses of 

communities at potentially affected Hudson River sites (HR02 

through HR05), and the biomasses of cutlips minnow, central 

mudminnow, smallmouth bass, and rock bass dominated at 

the control site HR01 (table 19, fig. 20). The biomasses of fish 

communities at sites HR01 and HR02 were not well balanced 

but were well balanced among several species at HR04 and 

HR05 (table 19, fig. 20). The overall effects of releases on 

the biomasses, like the densities, of fish communities in the 

Hudson River, include the additions of a few species, small 

or no decreases in total biomass, and a general increase in the 

balance of species as community equitability increases at sites 

farther downstream (table 17).

Macroinvertebrate Assemblages

Although macroinvertebrate data were summarized for 

surveys done in 2005 and 2006, only the results from 2006 

were interpreted because differences between data collected 

at the same sites in 2005 and 2006 were generally minor, 

and because the survey in 2006 included three additional 

sites in the Cedar River that were not sampled in 2005. Data 

Figure 19. Graph showing dDensity (number of fish per 0.1 hectare) of each fish group or 

species at 11 study sites on the Indian, Hudson, and Cedar Rivers, Adirondack Mountains, 

New York, 2005–06. Locations of study sites are shown in figure 1; study-site codes are listed 

in table 1.

0

500

1,000

1,500

2,000

2,500

CR01 CR02 CR03 CR04 IR01 IR02 IR03 HR01 HR02 HR04 HR05

SPECIES DENSIT

Y, IN

N

U

MBER PER 0.1 HECTARE 

Blacknose dace Longnose dace

Common shiner White sucker

Bullhead and madtom Brown and rainbow trout

Bass and sunfish Other minnows and sculpin

STUDY-SITE CODE
46 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06 Table 19. Estimates of biomass for each fish species collected at each of 11 study sites on the Indian, Hudson, and Cedar Rivers, Adirondack Mountains, New York, 2005–06. [Biomass measured in grams per 0.1 hectare. Locations of study sites are shown in figure 1. Unit conversions are shown in the conversion tables at the front of the report. Study-site codes are listed in table 1.] Common name Study sites CR01 CR02 CR03 CR04 IR01 IR02 IR03 HR01 HR02 HR04 HR05 Creek chub 5 384 64 11 0 0 0 0 0 10 0 Common shiner 145 1,444 79 56 0 0 0 0 0 0 152 Stonecat 0 0 0 0 0 0 0 80 0 0 0 Bluntnose minnow 0 67 0 14 0 0 0 0 0 0 0 Central mudminnow 0 0 0 5 0 0 0 114 0 0 0 Fallfish 0 0 0 0 0 0 0 20 24 140 104 Redbreast sunfish 0 0 0 77 83 0 0 31 0 0 0 White sucker 48 17 0 0 0 0 0 0 0 0 129 Cutlips minnow 0 0 381 429 0 788 65 138 43 23 378 Margined madtom 0 0 1,037 2 0 0 0 0 80 3 11 Brown bullhead 3 0 0 0 0 0 0 0 0 0 0 Brown trout 0 0 0 0 0 0 0 0 0 0 106 Rainbow trout 0 0 0 0 330 0 0 0 0 0 304 Northern redbelly dace 0 1 0 0 0 0 0 0 0 0 0 Blacknose dace 1,337 1,363 26 0 0 0 0 0 0 0 0 Longnose dace 0 212 74 133 0 68 46 0 5 3 54 Largemouth bass 0 0 0 0 9 0 0 0 2 0 0 Smallmouth bass 0 0 3 126 5 165 1,033 612 615 46 20 Rock bass 0 0 94 410 132 448 0 165 0 0 0 Slimy sculpin 0 0 0 0 0 127 99 0 0 0 5 Other minows 3 0 0 0 0 0 0 0 0 3 20 Totals 1,541 3,488 1,758 1,263 559 1,596 1,243 1,160 769 228 1,283
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 47

from 2006 on community indexes, functional feeding guilds, 

similarity of community assemblages, and dominant species 

were evaluated for 12 study sites in the Cedar, Indian, and 

Hudson Rivers to test hypotheses that the releases negatively 

affected macroinvertebrate communities at all Indian River 

sites and at the four downstream sites on the Hudson River. 

As in the fishery analyses, the four study sites in the Cedar 

River and HR01 in the Hudson River were used as controls. 

Because sites in the upper Cedar River were affected by a runof-the-river impoundment, comparisons of macroinvertebrate 

indexes between Indian River and Cedar River sites illustrate 

the relative effects of the releases from Lake Abanakee 

on benthic macroinvertebrate communities in the Indian 

River. The comparison of community indexes at the four 

downstream Hudson River sites (HR02–HR05) to indexes at 

HR01 and among each other help define the significant and 

possibly diminishing downstream effects caused by both the 

impoundment and recreational releases. If the releases are 

assumed to have only nominal effects on macroinvertebrate 

communities in the Hudson River, then comparisons of 

community indexes from the Hudson River and the Indian 

River sites should illustrate the combined effects that the 

impoundment and the releases have on communities at all 

three Indian River sites.

Community Indexes—Summaries of mean indexes and 

the NYSBAP for macroinvertebrate communities surveyed 

in 2005 and 2006 at all study sites are listed in table 20. 

Community richness fell at or below the lower (slightly 

impacted) threshold of 26 species (Smith and Bode, 2004) 

only at CR01 and the three Indian River sites during 2005 

and 2006, but low richness indicated slight effects at two 

additional Cedar River and three Hudson River sites sampled 

during 2006. The HBI upper threshold of 4.51 (Smith and 

Bode, 2004) was surpassed only at sites CR01 and IR01 

during 2005 and 2006. Estimates of EPT richness were at or 

below the lower (slightly impacted) threshold of 10 species 

(Smith and Bode, 2004) at IR01 in 2005 and at all Indian 

River sites and at CR01 and CR04 in 2006. Estimates of PMA 

were below the lower (slightly impacted) threshold of 64 

(Smith and Bode, 2004) at CR01, IR01, and IR02 in 2005 and 

remained so at these same sites and at CR04 and HR04 during 

2006. Except for HBI, the metrics categorized IR01 and CR01 

as moderately impacted (table 20). Because NYSBAP scores 

are derived from the four core metrics (above), the average 

scores at 12 sites indicate slight or no impacts (fig. 21). The 

NYSBAP scores below 7.5 indicate that macroinvertebrate 

communities were slightly impacted only at CR01 and IR01 

during 2005, but all three Indian River sites and CR01 and 

CR04 were slightly impacted during 2006 (table 20, fig. 21).

To correctly assess the effects of the releases from Lake 

Abanakee on downstream macroinvertebrate communities, 

it is important to recognize that the assemblages at such sites 

exhibit certain patterns normally associated with upstream 

impoundments. Changes in water quality, food supplies, 

loads of nutrients and suspended sediment, and temperatures 

downstream from dams generally produce considerable shifts 

Figure 20. Graph showing bBiomass (grams per 0.1 hectare) of each fish or species at 

11 study sites on the Cedar, Indian, and Hudson Rivers, Adirondack Mountains, New York, 

2005–06. Locations of study sites are shown in figure 1; study-site codes are listed in table 1.

0

500

1,000

1,500

2,000

2,500

3,000

3,500

CR01 CR02 CR03 CR04 IR01 IR02 IR03 HR01 HR02 HR04 HR05

SPECIES BIO

M

ASS, IN

GRA

MS PER 0.1 HECT

ARE 

Blacknose dace Longnose dace

Common shiner White sucker

Bullhead and madtom Brown and rainbow trout

Bass and sunfish Other minnows and sculpin

STUDY-SITE CODE
48 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

in species composition and resultant metrics (Bode and others, 

2002). For this reason, the effects of releases on communities 

at Indian River sites need to be qualified and separated from 

general effects caused mainly by the impoundment. For 

instance, macroinvertebrate metrics at sites downstream 

from impoundments are typically corrected by shifting 

the impact-category cutoffs down by one category (Bode 

and others, 2002). For the systems used in this study, the 

NYSBAP threshold of 7.5 between slightly and nonimpacted 

sites would decrease to 5.0; thus, communities at all sites 

would be reclassified as nonimpacted. In addition, leastsignificant-difference (LSD) 95-percent confidence intervals 

for mean 2006 NYSBAP scores (fig. 21) and comparisons of 

homogeneous groups (table 21) indicate that communities 

at Indian River sites IR01, IR02, and IR03, and Cedar River 

sites CR01 and CR04 are relatively alike, but that they differ 

from communities at most Hudson River sites. Communities 

at these sites also differed from those at all Hudson River 

sites. The fact that mean NYSBAP scores at sites IR03, CR03, 

and HR04 in 2006 do not differ significantly from each other 

(table 21) may be related to a diminished impoundment effect 

at IR03 and a further diminished impoundment effect at CR03 

and HR04. Both of these sites are situated downstream from 

long riverine pools, which in the case of CR04 resemble large 

bogs or marshes.

The lack of significantly different mean NYSBAP scores 

and other indexes between HR01 and the four other Hudson 

River sites downstream from its confluence with the Indian 

River during 2006 (table 21, fig. 21) and during 2005 (not 

shown) and the fact that all Hudson River sites were classified 

as nonimpacted during 2005 and 2006 (fig. 21) suggest that the 

releases and the impoundment had little or no negative effects 

on macroinvertebrate communities in the Hudson River. The 

fact that NYSBAP scores (and most other metrics) were not 

Table 20. Mean estimates for macroinvertebrate community richness, Hilsenhoff’s Biotic Index, Ephemeroptera-PlecopteraTrichoptera (EPT) richness, Percent Model Affinity (PMA), and the New York State Bioassessment Profile (NYSBAP) for 

samples collected in riffles at 12 study sites in the Cedar, Indian, and Hudson Rivers, Adirondack Mountains, New York, 

2005–06.

[HBI, Hilsenhoff’s Biotic Index; EPT, Ephemeroptera-Plecoptera-Trichoptera; PMA, Percent Model Affinity; NYSBAP, New York State 

Bioassessment Profile. Locations of study sites are shown in figure 1; unit conversions are shown in the conversion tables at the front of the report. 

Study-site codes are listed in table 1.]

Study 

site

Richness 

(number of species) HBI EPT richness( number of species)

PMA

(percent) NYSBAP

2005 survey

CR01 25.3 4.6 11.3 59.3 7.3

IR01 20.0 4.7 9.0 48.0 6.1

IR02 26.0 4.4 13.0 58.7 7.6

IR03 25.3 4.3 14.0 70.0 8.1

HR01 28.3 4.3 15.0 69.3 8.4

HR02 31.0 3.7 18.3 65.0 8.7

HR03 27.3 4.2 12.0 72.0 8.1

HR04 33.7 3.4 17.3 77.3 9.1

HR05 35.0 4.2 14.0 82.0 9.1

2006 survey

CR01 15.3 5.5 7.3 46.0 5.2

CR02 29.3 4.3 13.0 75.0 8.4

CR03 23.0 4.2 12.7 78.3 8.0

CR04 23.7 4.0 6.7 49.3 6.4

IR01 18.3 5.3 5.3 44.0 5.2

IR02 18.7 4.3 10.0 59.0 6.7

IR03 20.3 3.7 9.7 71.3 7.3

HR01 24.3 3.7 16.7 69.3 8.3

HR02 29.7 3.6 15.7 66.7 8.5

HR03 32.3 3.8 16.0 76.7 9.0

HR04 20.0 3.1 12.7 62.7 7.6

HR05 24.7 3.6 14.0 74.3 8.3
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 49

significantly different between Cedar River and Indian River 

sites immediately downstream from their respective dams 

further indicates that the factors that affect macroinvertebrate 

communities in both rivers were similar. Therefore, these 

results indicate that the recreational releases did not contribute 

substantially to impacts on macroinvertebrate communities 

of the Indian River. Observed effects were caused mainly 

by impounded lake waters (continuously released into the 

Indian River) and that these impoundment effects did not 

extend to sites in the Hudson River. The absence of significant 

community impacts, however, does not entirely eliminate 

the possibility that releases could have adversely affected 

individual species populations and that ensuing species 

replacements fundamentally altered local food webs and 

riverine ecosystems at one or more Indian River and Hudson 

River sites.

Functional Feeding Guilds—Further analyses of feeding 

guilds and differences in the dominant macroinvertebrate taxa 

at each study site generally confirm impoundment effects but 

also help reveal subtle effects that the releases might have had 

at the trophic and species-population levels. Spatial trends 

in the percentages of the five functional feeding guilds at 

the study sites in each river were generally similar in 2005 

and 2006 (table 22); thus, only the results from 2006 were 

examined in detail. Summaries of data in figure 22 show that 

percentages of collector-gathers and scrapers were lower at 

sites affected by impoundments (IR01, IR02, and CR01), and 

that percentages of collector-filterers at those sites were higher 

than at most unaffected sites farther downstream from both 

impoundments during 2006. The percentages of collectorfilterers at the upper two sites in the Indian River (IR01 and 

IR02) were generally comparable to percentages at CR01, and 

they were higher than percentages at all sites in the Hudson 

River during 2006 (fig. 22, table 22). The percentages of 

predators at all sites in the Indian River were slightly lower 

than at several sites in the Hudson River and at CR01 and 

CR02, but differences were typically not significant during 

2006 (table 23). The percentages of scrapers at all Indian 

River sites and at CR01 were 5.0 or less, lower than at CR02 

(14.3), and significantly lower than at the five Hudson River 

sites during 2006 (table 23). The percentages of scrapers at the 

three Indian River sites generally ranged from 0.3 to 1.7 and 

from 5 to about 18 at the four Cedar River sites in 2006. There 

were no major differences in the percentages of shredders 

among all study sites; however, the percentages of collectorgatherers were significantly lower at IR01, CR01, and CR04 

than at most other sites. Percentages of the five feeding guilds 

at HR01 did not differ significantly from those at the other 

four Hudson River sites.

Like the community indexes, the percentages of 

feeding guilds at CR01 and IR01, as well as those at IR02 

and IR03, provide strong evidence that the impoundments 

heavily affected food webs at riverine sites immediately 

downstream from both dams. The main difference between 

macroinvertebrate assemblages in the Cedar and Indian Rivers 

was that scrapers were generally absent at all Indian River 

2

4

6

8

10

CR01 CR02 CR03 CR04 IR01 IR02 IR03 HR01 HR02 HR03 HR04 HR05

NEW YORK STATE

BIOASSESSMENT PROFILE SCORE

0

No impact

Severe impact

Moderate impact

Slight impact

STUDY-SITE CODE

Figure 21. Graph showing Average New York State Bioassessment Profile scores and 95-percent 

confidence intervals for Fisher’s least significant difference in relation to impact categories at 12 sites 

surveyed in the Cedar, Indian, and Hudson Rivers, Adirondack Mountains, New York, August 2006. 

Locations of study sites are shown in figure 1; study-site codes are listed in table 1.
50 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06 Table 21. Mean estimates for macroinvertebrate community richness, Hilsenhoff’s Biotic Index (HBI), Ephemeroptera-Plecoptera-Trichoptera (EPT) richness, Percent Model Affinity (PMA), and the New York State Bioassessment Profile (NYSBAP) and similarities among 12 study sites in the Cedar, Indian, and Hudson Rivers, Adirondack Mountains, New York, 2006. [The columns of letters denote sites with homogeneous indexes (mean indexes were not significantly different (p < 0.05) among coindicated sites in the same vertical column) based on Fisher’s least significant difference procedures. Locations of study sites are shown in figure 1. Study-site codes are listed in table 1] Site code Mean richness Homogeneous rich- ness Mean HBI Homogeneous HBI Mean EPT Homogeneous EPT Mean PMA Homogeneous PMA Mean NYSBAP Homogeneous NYSBAP IR01 18.3 a b 5.3 f 5.3 a 44.0 a 5.2 a IR02 18.7 a b c 4.3 e 10.0 c d e 59.0 b 6.7 b c IR03 20.3 a b c d 3.7 b 9.7 b c d 71.3 d e f 7.3 c d HR01 24.3 d e 3.7 b 16.7 h 69.3 c d e 8.3 e HR02 29.7 f g 3.6 b 15.7 f g h 66.7 b c d 8.5 e f HR03 32.3 g 3.8 b c 16.0 g h 76.7 e f 9.0 f HR04 20.0 a b c d 3.1 a 12.7 d e f 62.7 b c 7.6 d HR05 24.7 d e f 3.6 b 14.0 f g h 74.3 d e f 8.3 e f CR01 15.3 a 5.5 g 7.3 a b c 46.0 a 5.2 a CR02 29.3 e f g 4.3 e 13.0 e f g 75.0 d e f 8.4 e f CR03 23.0 b c d 4.2 d e 12.7 d e f 78.3 f 8.0 d e CR04 23.7 c d 4.0 c d 6.7 a b 49.3 a 6.4 b
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 51

sites. Except for the near absence of scrapers, feeding-guild 

data provided little evidence that the releases had a significant 

and unique effect on macroinvertebrate communities in the 

Indian River or at any Hudson River site (downstream from 

the confluence with the Indian River).

The dominant and subdominant invertebrate species 

(the two to four species with the highest sample counts) 

shifted somewhat between affected and nonaffected sites, 

reflecting different physical conditions and food sources 

within riffles at study sites immediately downstream from 

impoundments on the Indian River and the Cedar River 

during 2005 and 2006. Collector-gatherers (for example, 

swimming mayflies—Ameletus spp. and Acentrella spp.), 

scrapers (for example, baetid mayflies such as Heterocloeon 

sp. and beetle larvae—Oulimnius spp. and Stenelmis spp.), 

predators (for example, Acariformes and Megalopterans such 

as Climacia sp.), and collector-filterers, such as fingernail 

and pea clams (Musculium transversum and Pisidium 

compressum) and the stonefly (Hydropsyche spp.), typically 

dominated macroinvertebrate communities at HR01, HR02, 

and HR03, even though flows at these sites fluctuated widely 

with releases. Collector-filterers including the pea clam 

P. compressum, blackflies (Simulium gouldingi), net-building 

chiromonids (Microspectra polita), and caddisflies (for 

example, Hydropsyche spp. and Nyctiophylax sp.) dominated 

local communities at CR01, IR01, and to some extent at 

CR04 (fig. 22). Although two species (Pisidium compressum

and Simulium gouldingi) were abundant at IR01, they were 

almost entirely absent at CR01. Scrapers, such as Stenelmis 

spp., Oulimnius spp., Phaenopsectra sp., Heterocloeon sp., 

and Stenonema spp., were present at both sites, but they 

constituted only 5 percent of total counts at CR01 in 2006 

and less than 2 percent of counts at IR01 during 2005 and 

2006 (table 23). Communities at other Indian River and Cedar 

River sites (IR02, IR03, CR02, and CR03) were similar to 

each other and more similar to those at Hudson River sites 

than to communities at other affected sites within both rivers 

during 2006. The predominance of collector-filterers only at 

CR01 and IR01 confirms that the effects are spatially limited 

and directly related to conditions normally encountered below 

Table 22. Percentage compositions of five functional feeding groups in macroinvertebrate communities at 12 study sites in 

the Cedar, Indian, and Hudson Rivers, Adirondack Mountains, New York, 2005–06.

[Locations of study sites are shown in figure 1; study-site codes are listed in table 1.]

Study 

code

Collectorfilterer Predator Scraper Shredder Collectorgatherer

2005 

CR01 17.7 51.3 19.8 3.1 8.1

IR01 51.5 33.2 2.7 1.0 11.5

IR02 46.0 19.3 2.3 5.7 26.7

IR03 34.6 23.2 3.8 2.8 35.7

HR01 31.3 26.3 17.7 4.7 20.0

HR02 24.4 29.1 20.4 6.4 19.7

HR03 25.0 32.8 19.8 1.3 21.1

HR04 19.8 30.2 21.1 8.7 20.1

HR05 12.8 24.6 19.6 7.1 36.0

2006 

CR01 66.7 21.3 5.0 3.3 3.7

CR02 9.7 25.7 14.3 6.7 43.7

CR03 14.0 16.0 9.7 2.0 58.3

CR04 56.7 15.3 17.7 3.0 7.3

IR01 66.9 20.9 1.4 2.0 8.8

IR02 47.3 17.3 0.3 5.3 29.7

IR03 33.8 16.5 1.7 0.3 47.6

HR01 28.3 25.3 23.3 1.7 21.3

HR02 29.0 28.3 18.3 2.0 22.3

HR03 19.1 34.8 18.4 3.3 24.4

HR04 22.0 20.0 25.0 2.0 31.0

HR05 21.4 28.4 18.4 2.0 29.8
52 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

impoundments (Bode and others, 2002). The comparable and 

limited effects on communities in both the Indian and Cedar 

Rivers (within the first few hundred meters downstream from 

the respective dams) and the relatively similar communities at 

IR02–03, CR02–03, and all Hudson River sites indicate that 

the releases did not cause unique effects on macroinvertebrate 

communities in most of the lower Indian River or at any study 

site in the Hudson River. The larger percentage of scrapers 

at CR01 than at IR01, IR02, and IR03 and the occurrence of 

two collector-filterer species only at IR01 indicate, however, 

that the releases did have some effect on macroinvertebrate 

assemblages in the Indian River, primarily at the reach closest 

to the Abanakee Dam.

Community Similarity—A cluster analysis of Bray-Curtis 

similarities (fig. 23) for 2006 macroinvertebrate data generally 

supports prior findings from analyses of feeding guilds and 

dominant species. The macroinvertebrate assemblages at 

sites IR01 and CR01 did not differ significantly (p < 0.05) 

from one another and were more similar to each other (about 

45 percent similar) than to assemblages at all other study sites 

(about 29 percent similar). Macroinvertebrate assemblages at 

IR02 and IR03 were about 54 percent similar to each other, 

29 percent similar to those at CR01 and IR01, and about 

32 percent similar to assemblages at the remaining study sites. 

Assemblages at CR02, CR03, and CR04 were 38 to 58 percent 

similar to each other and 43 percent similar to those at all 

Hudson River sites. Macroinvertebrate assemblages at all 

Hudson River sites were 53 to 65 percent similar to, and not 

significantly different from, assemblages at each site (fig. 23).

The 40-percent similarity bubbles in the two-dimensional 

ordination plot (fig. 24) graphically show how assemblages of 

macroinvertebrate species from sites that are affected, partly 

affected, or unaffected segregate into distinctive classes. These 

associations do not indicate any unique effects of the releases 

on communities the Indian River. They do, however, indicate 

strong and similar impoundment effects on communities at 

only two sites, IR01 and CR01 (each immediately downstream 

from a dam); an undefined effect at CR04 (54 km below the 

dam); similar and diminishing effects at Indian River sites 

IR02 and IR03 (2 to 4 km below the dam); minor or no effects 

at Cedar River sites CR02 and CR03 (8 to 54 km below the 

dam); and no distinguishable effects at all Hudson River sites.

In summary, the general function (integrity or health) 

of macroinvertebrate communities at all Indian, Cedar, and 

Hudson River sites was not seriously affected by water 

quality, which ranged from very good to good (Novak and 

Bode, 1992; Smith and Bode, 2004). Comparable effects 

on the structure of macroinvertebrate communities at sites 

immediately downstream from both dams (IR01 and CR01) 

could be attributed to the unique nature of impoundment 

waters. The near absence of scrapers at all Indian River sites 

and the presence of two species (blackflies and pea clams) 

only at IR01 indicate that the releases from Lake Abanakee 

had minor effects on the structure of macroinvertebrate 

communities only at IR01. The consequences that these minor 

effects could have on organisms at higher trophic levels, 

however, were not investigated in this study.

0

20

40

60

80

100

CR01 CR02 CR03 CR04 IR01 IR02 IR03 HR01 HR02 HR03 HR04 HR05

PERCENTAGE IN EACH FUNCTIONAL FEEDING GROUP

Collector-gatherer

Shredder

Scraper

Predator

Collector-filterer

EXPLANATION

STUDY-SITE CODES

Figure 22. Graph showing tThe percentages of macroinvertebrates in each of five functional feeding groups at 12 

sites surveyed in the Cedar, Indian, and Hudson Rivers, Adirondack Mountains, New York, August 2006. Locations of 

study sites are shown in figure 1; study-site codes are listed in table 1.
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 53 Table 23. Mean percentages of macroinvertebrate community feeding groups and similarities among 12 study sites in the Cedar, Indian, and Hudson Rivers, Adirondack Mountains, New York, 2006. [The columns of letters denote sites with homogeneous feeding groups (mean indices were not significantly different (p < 0.05) among coindicated sites in the same vertical column) based on Fisher’s least significant difference procedures. Locations of study sites are shown in figure 1; study-site codes are listed in table 1.] Study site Collector- filterer Homogeneous collector-filterer Predator Homogeneous predator Scraper Homogeneous scraper Shredder Homogeneous shredder Collector- gatherer Homogeneous collector-gatherer IR01 66.9 h 20.9 a b c 1.4 a b 2.0 a b 8.8 a IR02 47.3 f 17.3 a b 0.3 a 5.3 c d 29.7 c IR03 33.8 e 16.5 a b 1.7 a b 0.3 a 47.6 e CR01 66.7 h 21.3 a b c 5.0 b 3.3 b c 3.7 a CR02 9.7 a 25.7 b c d 14.3 d 6.7 d 43.7 e CR03 14.0 a b 16.0 a b 9.7 c 2.0 a b 58.3 f CR04 56.7 g 15.3 a 17.7 d 3.0 a b c 7.3 a HR01 28.3 d e 25.3 a b c d 23.3 e 1.7 a b 21.3 b HR02 29.0 e 28.3 c d 18.3 d 2.0 a b 22.3 b c d HR03 19.1 b c 34.8 d 18.4 d 3.3 b c 24.4 b c d HR04 22.0 c d 20.0 a b c 25.0 e 2.0 a b 31.0 d HR05 21.4 c 28.4 c d 18.4 d 2.0 a b 29.8 d
54 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

Figure 23. Graph showing cCluster analysis of Bray-Curtis similarities for macroinvertebrate assemblages based 

on square-root-transformed relative abundance data from 3 combined replicates collected at each of 12 sites in the 

Cedar, Indian, and Hudson Rivers, Adirondack Mountains, New York, August 2006. The red links identify sites at which 

replicates did not differ significantly (p ≤ 0.05) from each other. Locations of study sites are shown in figure 1; study-site 

codes are listed in table 1.

CR01

IR01

IR02

IR03

CR04

CR02

CR03

HR03

HR04

HR05

HR01

HR02

STUDY-SITE CODE

100 80 60 40 20

BRAY-CURTIS SIMILARITY, IN PERCENT

40-percent similarity

60-percent similarity

CR02 CR01

CR03

CR04

HR01

H HR02 R03

HR04

HR05

IR01

IR02

IR03

EXPLANATION

Figure 24. Diagram of oOrdination plot of macroinvertebrate assemblages based on square-root-transformed relative 

abundance data from 3 combined replicates at each of 12 sites in the Indian, Hudson, and Cedar Rivers, Adirondack 

Mountains, New York, August 2006. The bubbles denote significant group membership (40 and 60 percent Bray-Curtis 
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 55

Trout Behavior

Results that summarize the use of thermal refuges, 

effects of the releases, movement behavior, persistence 

(apparent survival), and final location of transmitters for trout 

tracked during the telemetry study are listed and discussed 

separately below.

Use of Thermal Refuges—The percentage of transmitter 

observations of trout temperatures cooler than nearby mainstem river waters was used to approximate the percentage 

of time that trout used potential thermal refuges and the 

percentage of trout that used potential refuges at study reaches 

in the three rivers. Percentages generated on the basis of TDs 

of -1°C (trout were at least 1°C cooler than the main-stem 

river) were considered liberal estimates of refuge use, whereas 

percentages calculated on the basis of TDs of -2oC (trout were 

at least 2°C cooler than the main-stem river) were treated as 

conservative estimates of refuge use. During 2005 and 2006, 

21.7 percent of all trout-temperature observations were at 

least 1oC cooler than water temperatures in the Cedar River, 

as were 3.9 percent of observations for the Indian River and 

28.8 percent of observations for the Hudson River (table 24) 

(the percentages shown do not include data from time blocks 

during which temperatures might have been affected by 

releases). Using TDs that were at least 2oC cooler than river 

temperatures for both years, mean percentages were found to 

decrease to about 11.3 percent of observations in the Cedar 

River, 2.7 percent in the Indian River, and 12.2 percent in the 

Hudson River (table 24). The percentages of TDs that were 

greater than or equal to -1oC and -2oC during the three time 

blocks on both nonrelease and release days for the three study 

reaches (rivers) are shown in figures 25 and 26, respectively. 

Interpreting the relations between TDs and releases (and 

assessing the effects of the releases) is problematic because 

the thresholds selected to indicate use of thermal refuges were 

somewhat subjective.

A comparison of mean TDs with Fisher’s LSD 95-percent 

confidence intervals (CIs) for all trout tracked in each of the 

study reaches helped determine the appropriate TD cutoffs 

for refuge use and also showed how well the observations 

represented the actual percentage of time that trout used 

refuges (or the percentage of trout that appeared to be using 

refuges). Mean TDs and 95-percent LSD CIs for all telemetry 

trout tracked in the Hudson River during 2006 (fig. 27) 

showed that 5 out of 16 trout had TDs that were at least 1oC 

cooler than the main-stem waters, and that the mean TD did 

not extend lower than -2oC for all trout (trout number 51 was 

excluded because there were only two observations for it). 

The clear separation of TDs for the 5 (or 6) trout from the 

other 10 (TDs for which ranged around 0) indicates that the 

threshold of 1oC TD may be appropriate to categorize the 

number and percentage of trout or the percentage of time that 

trout were using thermal refuges. Even though categories 

were more obvious in 2006 than in 2005, about 24 percent of 

telemetry trout in the Hudson River were classified as using 

thermal refuges during both years. Similar relations held for 

trout in the Cedar River, where 21.4 percent of telemetry trout 

(3 out of 14) during 2006 were classified as using thermal 

refuges (no tracking was done in 2005). In the Indian River, 

8.3 percent of telemetry trout (2 out of 24) were at least 

1oC cooler than the river during 2005 and 2006 and were 

classified as using thermal refuges at least part of the time. The 

percentages of trout that were 1oC (or more) cooler than mainstem rivers were similar to percentages of trout with TDs of 

-1oC (and not -2oC), which suggests that all observations may 

be used to evaluate the effects of the releases on the use of 

thermal refuges by brown trout in the three study reaches.

The benefit that thermal refuges potentially provide 

to resident and stocked trout differs among the three rivers 

and has some important implications. First, the percentage 

of trout using thermal refuges was very low in the Indian 

River (3.9 percent) and moderate (21.7 to 28.8 percent) in the 

Hudson and Cedar Rivers. Inequalities in the quantity, quality, 

or accessibility of thermal refuge areas and disparities in other 

environmental factors (for example, the presence of deep, 

slow-water habitat or the availability of prey) may account 

for differences in trout behavior between rivers. Comparable 

estimates of refuge usage in the Cedar and Hudson Rivers 

indicate that thermal refuges are widespread and available 

to trout in both study reaches. This study was not designed 

to directly quantify how low or moderate usage of thermal 

refuges might affect survival of individual trout in the three 

rivers. Potential refuge areas that are cooler than the mainstem river but remain warm enough to be stressful may be able 

to prolong the life of trout by reducing cumulative exposure; 

however, such refuges might not be able to sustain trout during 

prolonged periods of thermal stress.

Second, the percentages of all trout-temperature 

observations that were lower than 20oC (fig. 28) on both 

release and nonrelease days confirm that thermal conditions 

were different within the three study reaches. These 

differences might affect trout survival and their need for 

and use of thermal refuges. On average, 45.7 percent of 

trout-temperature observations in the Cedar River in 2006 

and 3.1 percent in the Indian River and 14.5 percent in 

the Hudson River were 20°C or cooler in 2005 and 2006 

(fig. 28, table 24) during time blocks normally affected by the 

releases. Differences in the percentages of trout-temperature 

observations at (or warmer than) stressful temperatures reflect 

differences in the quality or quantity of thermal refuges and 

preferred physical habitat (in absolute values), the diurnal 

variation in ambient river temperatures, and (or) in the 

extent to which releases reduce the amount or availability 

of thermal refuges in the three rivers. The percentages 

of trout-temperature observations of river temperatures 

greater than 20oC and trout temperatures cooler than the 

river by at least 1oC decreased to 29.7 percent in the Cedar 

River and increased to 4.0 percent in the Indian River and 

to 33.0 percent in the Hudson River. These increases may 

indicate an increased use of thermal refuges in the Indian and 

Hudson Rivers when main-stem water temperatures become 

stressful. The percentages decreased to 17.1 percent in the 
56 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

Cedar River, 1.2 percent in the Indian River, and 8.9 percent 

in the Hudson River when river temperatures were greater 

than 20oC and trout were both cooler than 20oC and cooler 

than the river by more than 1oC (table 24). If the number of 

observations was assumed to be roughly comparable to the 

percentage of time trout spent in refuges or the percentage of 

trout that spent any time in refuges, the final estimates may 

represent the maximum percentage of trout that were able 

to maintain nonstressful body temperatures either by chance 

or by using thermal refuges in the three reaches. Thus, the 

actual percentages of trout that used and directly benefited 

from thermal refuges when river temperatures were stressful 

and body temperatures were within their preferred range 

appeared to be substantially lower than that indicated by 

analysis of observations of all TDs that were at least -1oC 

cooler than main-stem waters. Differences in fish behavior or 

geographic or physical conditions in the Cedar and Hudson 

Rivers apparently enable a larger fraction of stocked trout (and 

probably resident trout) to effectively avoid thermal stresses 

(which should be reflected in better growth and survival rates) 

than was possible in the Indian River. Other factors, such as 

primary productivity, preferred habitat, and fishing pressure 

may also affect trout growth and survival but are beyond the 

scope of this investigation.

Effects of Recreational Releases—The effects of 

flow releases on the use of thermal refuges by trout were 

evaluated on the basis of (1) multilevel-effect models for a 

statistical analysis of the differences in TDs in the Cedar River 

and in the two rivers affected by releases, (2) a qualitative 

assessment of TDs during release and nonrelease days for 

each river, and (3) a qualitative assessment of trout body 

temperatures spanning the period before and during releases. 

Both qualitative analyses make no attempt to account for 

biases caused by repeated measures of individual trout or for 

sampling bias caused by the limited range of the fixed receiver 

for detecting transmitter signals.

Multilevel-effect models were used to provide a 

defensible quantitative analysis of the effects of releases on 

the use of refuges by trout, evaluate additional factors that 

may affect use of thermal refuges in all three study rivers, and 

confirm that stocked trout use thermal refuges. As originally 

hypothesized, release day was not as important as other 

variables for explaining variation in TDs in the Cedar River, 

but release day was important for the Indian and Hudson 

Rivers. Even so, release day had explanatory power only 

during time blocks when the release bubble passed through 

the reach: midday for the Indian River and afternoon for the 

Hudson River (table 24). Although most results from each 

study reach in each river were predictable, several important 

relations and deviations from expected results warranted more 

detailed analysis and explanation (Boisvert, 2008).

Telemetry-derived TDs for trout in the Cedar River 

provide a reference against which to compare and validate 

findings from the Indian and Hudson Rivers, which were 

affected by releases. The most important variable during all 

times of day (morning, midday, and afternoon) in the Cedar 

River was the interaction between ambient river temperature 

and whether a trout was near or not near a tributary (table 24). 

The interaction indicates that the correlation of TD with one of 

the interacted predictor variables varied based on the value of 

that variable in the interaction. Although the variable “release 

day” had one of the three highest parameter weights for 

each time block, that weight was minor relative to the other 

parameters with higher predictor weights. For example, during 

the afternoon (TB3), daily mean discharge and interaction 

between river temperature and nearness to a tributary were 

both more than twice as important for explaining variation in 

TDs than was release day.

During morning (TB1) and midday (TB2) time blocks 

in the Cedar River, variation in TDs was explained best by 

models that included interaction between river temperature 

and nearness of a trout to a tributary (F1,170 = 48.76, 

Table 24. Percentages of all morning, midday, and afternoon observations of trout body temperatures made in the Cedar River 

(2006) and the Indian and Hudson Rivers (2005–06) when trout body temperatures were less than 20°C, cooler than the main stem 

by at least 1°C, cooler than the main stem by at least 2°C, cooler than the main stem by at least 1°C when river temperatures 

were greater than 20°C, and less than 20°C and also cooler than the main stem by at least 1°C when river temperatures were 

greater than 20°C.

[Temperature difference (TD) data from release days (and time blocks) that could be affected by releases were not included in Hudson River or Indian 

River calculations. °C, degrees Celsius] 

Study reach

Percentage of observed trout temperatures

All river temperatures River temperatures greater than 20°C

Less than 20°C At least 1°C 

cooler than main stem

At least 2°C 

cooler than main stem

At least 1°C 

cooler than main stem

Less than 20°C 

and at least 1°C 

cooler than main stem

Cedar River 45.7 21.7 11.3 29.7 17.1

Hudson River 14.5 28.8 12.2 33.0 8.9

Indian River 3.1 3.9 2.7 4.0 1.2
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 57

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

nonrelease

Morning (TB1) Midday (TB2) Afternoon (TB3)

34.6

13.3

31.2 30.8

27.3

23.5

1.2 2.4

5.7

1.7

4.2 5.5

13.5

7.3

17.0 18.1

31.7 33.5

A Cedar River

B Indian River

C Hudson River

PERCENTAGE

OF TEMPERATURE DIFFERENCES

GREATER THAN OR EQUAL TO -1 DEGREE CELSIUS

release

TIME BLOCK

EXPLANATION

Figure 25. Graphs showing pPercentages of temperature 

differences that were greater than or equal to -1o Celsius on 

nonrelease days within time blocks TB1, TB2, and TB3 in the 

A, Cedar River (2006), B, Indian River (2005–06), and C, Hudson 

River (2005–06), Adirondack Mountains, New York. Gray 

backgrounds indicate time blocks when the release bubble 

passed through study reaches in the Indian River (TB2) and 

Hudson River (TB3) on release days.

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

Morning (TB1) Midday (TB2) Afternoon (TB3)

A Cedar River

B Indian River

TIME BLOCK

C Hudson River

PERCENTAGE

OF TEMPERATURE DIFFERENCES

GREATER THAN OR EQUAL TO -2 DEGREES CELSIUS

nonrelease

release

EXPLANATION

7.7

10.0

15.6

11.7

14.3

7.8

0.0

2.4

5.0

1.1

3.5 1.6

5.4 5.5

8.2 7.6

18.3 18.0

Figure 26. Graphs showing pPercentages of temperature 

differences that were greater than or equal to -2o Celsius on 

nonrelease and release days within time blocks TB1, TB2, and 

TB3 in the A, Cedar River (2006), B, Indian River (2005–06), and 

C, Hudson River (2005–06), Adirondack Mountains, New York. 

Gray backgrounds indicate time blocks when the release bubble 

passed through study reaches in the Indian River (TB2) and 

Hudson River (TB3) on release days.
58 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

p < 0.01 for TB1 and F1,287 = 14.27, p < 0.01 for TB2). 

These models had almost 3–5 times more support than 

the next best model within each of the three model sets, 

and the fixed effect explained a significant amount of the 

variability. The best supported model for the afternoon 

in the Cedar River included the interaction between river 

temperature and nearness to a tributary and the variable mean 

daily discharge. This model was more than twice as well 

supported as the next best supported model. Both variables 

explained a significant amount of variation in TDs (daily 

mean discharge, F1,18.7 = 13.32, p < 0.01; interaction of 

river temperature with nearby tributary, F1,275 = 12.29, 

p < 0.01). Furthermore, differences between least-square mean 

(LSMean) estimates revealed that all of the less supported 

models that included release day were not significant for the 

Cedar River. Examination of LSMean estimates from the best 

supported model for TB3 (fig. 29A) reveals that, in general, 

trout temperatures were lower (trout were significantly cooler) 

than river temperatures that reached thermally stressful levels 

when the trout were within 50 m of a tributary. Although trout 

were probably using several types of thermal refuges, these 

findings indicate that tributary confluences are an important 

resource for trout. Results for morning and midday time 

blocks showed similar trends (Boisvert, 2008); however, the 

proximity of trout to a tributary did not strongly affect TDs 

when river temperatures were below 20oC. These findings do 

not address the effects of releases, but they show that trout 

used thermal refuges mainly when river temperatures were 

elevated, tributaries were likely an important source of thermal 

refuges, and the study design successfully captured the effects 

of environmental variables with no biases for release-day type.

TROUT IDENTIFIER

TEMPERATURE DIFFERENCE,

IN DEGREES CELSIUS

41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Figure 27. Graph showing aAverage differences between trout and river temperatures and standard 

errors for all observations of 17 trout tracked in the Hudson River, Adirondack Mountains, New York, 

during 2006. Trout identifier refers to the last two digits of the frequency of each implanted transmitter.

Recreational releases affected use of thermal refuges by 

trout in the Indian River as originally hypothesized (fig. 29B). 

Despite the relatively few tributaries and fewer observations 

of trout near tributaries in the Indian River, nearness to a 

tributary was more than five times more important than 

any other parameter during the time blocks before (TB1) 

and after (TB3) the release had passed through the reach 

(table 24). The best supported model during the morning 

and afternoon time blocks included only one fixed effect, 

nearness to a tributary (F1,231 = -5.61, p = 0.02 for TB1, and 

F1,226 = 23.82, p < 0.01 for TB3). Similarly, when much of 

the Indian River was inundated by high (release) flows during 

midday (TB2), the most important parameters (both had 

equal weights) were nearness to a tributary (F1,282 = 8.43, 

p < 0.01) and an interaction between river temperature and 

release day (F1,273 = 12.07, p < 0.01). These models had 

roughly 49 times more support than the second best supported 

model. Trout TDs varied little in the Indian River because 

thermoregulation (using thermal refuges) was rare, but trout 

near tributaries were cooler on average than the river during 

all time periods. Release day, during TB2, was correlated 

with reduced trout thermoregulation (TDs were more 

negative on release days) only when river temperatures were 

thermally stressful (fig. 29B); however, only about 1 percent 

of observations indicate that trout were in high-quality 

thermal refuges (trout temperatures < 20oC) when Indian 

River temperatures were stressful (>20oC) (table 24). These 

results indicate that tributary habitat is important for trout 

thermoregulation and that releases adversely affect the ability 

of trout to thermoregulate in the Indian River. These findings 

support the original hypotheses; however, the limited number 

or size of thermal refuges, small number of trout found in 
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 59

refuges, and nominal trout TDs (generally less than -0.5oC) 

within this study reach indicate that the releases have no clear 

effect on brown trout stocked into the lower Indian River.

In contrast to the Indian River, the releases had a 

moderate effect on use of thermal refuges by trout in the 

Hudson River (fig. 29C). Sufficient data were available for 

analysis of only the midday and afternoon time blocks. Like 

the Cedar River, the most important parameter during the 

midday time block (before the release bubble inundated 

Hudson River study reaches) was the interaction between 

river temperature and nearness (of trout) to a tributary 

(table 25). Although release day had the second greatest 

predictor weight, it did not explain a significant amount 

of the variation in TDs. As hypothesized, release day was 

included in the most important parameter (the interaction 

among river temperature, nearness to a tributary, and release 

day (F1,143 = 1.66, p < 0.01)) during the afternoon, when 

the release bubble affected the reach. Daily mean discharge 

(F1,275 = 12.12, p < 0.01) and distance (of trout) from a 

datalogger (F1,168 = 1.14, p = 0.29) also became important 

parameters during the afternoon as they did in the Cedar 

River. The model with the most support during midday 

included the interaction between release day and nearness to 

a tributary (F1,119 = 18.78, p < 0.01), and distance of trout 

to the nearest datalogger (F1,111 = 5.28, p = 0.02). The best 

supported model during the afternoon included an interaction 

among river temperature, nearness to a tributary, and 

release day (F1,143 = 1.66, p < 0.01); daily mean discharge 

(F1,275 = 12.12, p < 0.01); and distance to the nearest 

datalogger (F1,168 = 1.14, p = 0.29). Inspection of LSMean 

estimates from the best supported models for TB3 (fig. 29C) 

shows that trout temperatures were generally lower than river 

temperatures when the trout were thermally stressed. Under 

stressful river temperatures, trout were significantly cooler 

than the river when they were within 50 m of a tributary, 

but the magnitude of thermal relief was reduced (TDs were 

smaller) on release days. Nearness to a tributary generally 

did not affect trout TDs when river temperatures were close 

to 20oC. Results for TB2 in the Hudson River were similar to 

those for TB2 in the Cedar River when trout were undergoing 

thermal stress, indicating that conditions were similar in 

the two rivers on nonrelease days. Results for TB3, when 

releases affected the Hudson River study reach, indicate that 

the releases adversely affected thermoregulation of individual 

trout even when they were near tributaries.

A qualitative analysis that compares the percentages of 

observations with TDs greater than -1oC (trout were more 

than 1oC cooler than the river) on release days to those on 

nonrelease days approximates the proportion of trout adversely 

affected by releases and confirms the findings of multileveleffect models. This analysis also helps illustrate the biological 

relevance of the releases. Most of the following results are 

based on -1oC TDs because prior analyses of the percentages 

of observations of TDs of at least -1oC (and the mean TDs 

with their 95-percent LSD confidence intervals for individual 

trout) showed that the percentages of thermoregulating trout 

PERCENTAGE

OF TROUT TEMPERATURES LOWER THAN 20 DEGREES CELSIUS

19.2 23.3

10.4

19.2

6.5

14.4

52.7

65.5

50.3 48.5

27.5

37.1

2.5

7.7

1.4 2.8 0.7 2.4

0

20

40

60

80

100

0

20

40

60

80

100

0

20

40

60

80

100

nonrelease

release

EXPLANATION

Morning (TB1) Midday (TB2) Afternoon (TB3)

A Cedar River

B Indian River

TIME BLOCK

C Hudson River

Figure 28. Graphs showing pPercentage of observations of trout 

temperature lower than 20oCelsius on nonrelease and release 

days within time blocks TB1, TB2, and TB3 in the A, Cedar River 

(2006), B, Indian River (2005–06), and C, Hudson River (2005–06), 

Adirondack Mountains, New York. Gray backgrounds indicate time 

blocks when the release bubble passed through study reaches in 

the Indian River (TB2) and Hudson River (TB3) on release days.
60 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

A Cedar River

C Hudson River

B Indian River

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

Greater than 50 meters

from tributary

Less than 50 meters

from tributary

p = 1.37

RIVER TEMPERATURE =20°C 

p < 0.01

p = 2.63

p = 0.17

p = 3.58

RIVER TEMPERATURE =24°C 

p = 0.49

RIVER TEMPERATURE =20°C 

p = 0.02

Release day

Nonrelease day

p = 0.75

p < 0.01

p = 0.02

p = 0.07 p = 0.01

p = 0.07

p = 0.02

p = 0.14

p = 0.19

RIVER TEMPERATURE =19°C RIVER TEMPERATURE =24°C 

RIVER TEMPERATURE =25°C 

Greater than 50 meters

from tributary

Less than 50 meters

from tributary

Greater than 50 meters

from tributary

Less than 50 meters

from tributary

Greater than 50 meters

from tributary

Less than 50 meters

from tributary

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

ESTIMATED TEMPERATURE DIFFERENCE, IN DEGREES CELSIUS

EXPLANATION

Figure 29. Graphs showing eEstimated least-square mean temperature differences and standard errors calculated from 

the best supported multilevel model for the A, Cedar and B, Indian Rivers, Adirondack Mountains, New York, during the 

afternoon time block (TB3), and the C, Hudson River during the midday time block (TB2) during 2006. Interactions terms, 

denoted by multiple estimates, included river temperature and (or) release day and proximity to tributaries. The results of 
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 61

were roughly equivalent to the percentage of observations 

in which TDs were at least -1oC. As part of the analysis, 

the number of observations indicating that trout were 

thermoregulating is assumed to represent the approximate 

percentage of trout that were using thermal refuges (fig. 25). In 

the unaffected Cedar River, the percentage of trout cooler than 

20oC was highest in the morning (TB1), and these percentages 

decreased throughout the later (warmer) parts of the day 

(fig. 28), even though the percentage of trout using thermal 

refuges increased throughout the day (fig. 25). These data 

largely support the statistical results from the multilevel-effect 

models. Trout TDs decreased during time blocks when the 

release bubble affected study reaches in the Indian and Hudson 

Rivers (fig. 25). Trout with TDs of at least -1oC decreased 

from 5.7 percent on nonrelease days to 1.7 percent on release 

days during TB2 in the Indian River, and from 27.3 percent 

to 23.5 percent during TB3 in the Hudson River. These 

declines indicate that the releases decreased the utilization of 

thermal refuges by trout in both rivers. Such declines could 

be detrimental to trout survival when river temperatures are 

stressful. The small percentage (and number) of trout affected 

in the Indian River, however, indicates that few trout are using 

refuges under any thermal conditions. Therefore, adverse 

effects of the release on the sustainability of stocked trout in 

the Indian River are likely to be limited. The percentage of 

trout using refuges appears to be higher in the Hudson River 

than in the Indian River; however, the 3.8-percent decrease in 

usage during releases indicates that any effects of the releases 

on stocked trout (and possibly local trout populations) in the 

Hudson River should also be nominal (fig. 25C).

One apparent contradiction between the percentage 

analyses of TDs and the multilevel-model analysis emerges 

from TD data for the morning time block (TB1) in the Cedar 

and the Hudson Rivers. Unexpected differences between 

the percentages of trout using refuges on release days and 

on nonrelease days were found in both rivers; this indicates 

that behavioral thermoregulation decreased on release days 

(fig. 25), even though no releases occurred in the Cedar River, 

and releases occurred later in the day in the Hudson River. 

Results from the multilevel model, however, indicate that there 

were insufficient data for the TB1 in the Hudson River from 

which to draw statistically sound conclusions about release 

effects, and that TDs between release and nonrelease days 

during the morning in the Cedar River were accounted for by 

other more important variables (for example, river temperature 

and nearness to a tributary) (table 25). Release day was a 

relatively unimportant factor for the Cedar River models 

because it did not explain a significant amount of variability 

in thermoregulation. Although releases had the potential to 

strongly affect the use of thermal refuges and trout survival 

in the Hudson River and the Indian River, most findings 

indicated that trout generally utilized thermal refuges more 

frequently in the Hudson River than the Indian River but that 

the releases caused only small decreases in thermoregulation 

of trout in both rivers. Thus, the releases appeared to have no 

consequential effect on the use of thermal refuges by stocked 

trout in either the Hudson or Indian Rivers.

Changes in the body temperatures of several trout in the 

time spans before and during inundation by release bubbles 

in Hudson and Indian River study reaches (fig. 30) were also 

assessed qualitatively. This analysis focused only on changes 

Table 25. The relative importance (indicated with a predictor weight between 0 and 1, representing the likelihood 

that a parameter is the most important for explaining variability in temperature differences) of the three most important 

parameters for each river and time-block combination. 

[rivT, river temperature; ntrib, nearness to a tributary; rel, release day; dmd, daily mean discharge; * an interaction of variables, Shaded cells 

indicate the time period during which the release bubble passed through the river reach; parameters that include the variable release day are 

in bold]

Time block

Predictor weights and parameters

Cedar River Indian River Hudson River

Morning (TB1) rivT*ntrib = 0.97

rel = 0.18

rivT*ntrib*rel = 0.03

trib = 1.00

rel = 0.18

rivT = 0.06

Insufficient data

Midday (TB2) rivT*ntrib = 0.98

rel = 0.22

dmd = 0.02

trib = 0.98r

rivT*rel = 0.98

rel = 0.02

rivT*ntrib = 0.86

rel = 0.39

rivT*ntrib*rel = 0.14

Afternoon (TB3) rivT*ntrib = 0.93n

dmd = 0.76

rel = 0.34

trib = 1.00

rivT = 0.15

rel = 0.15

rivT*ntrib*rel = 0.94

dmd = 0.88

rivT = 0.04
62 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

in trout temperature over time; no direct comparisons to river 

temperatures were made. River temperatures reached at least 

20oC on all release and nonrelease days, however, and it was 

assumed that ambient river temperatures were not altered by 

release bubbles. Trout body temperatures in the Indian River 

did not change rapidly over time on nonrelease days, but 

increased abruptly on release days in 2 of 10 trout (fig. 30A), 

indicating that the release bubble reduced thermoregulation 

in at least two individuals. Although there appeared to be 

an effect, the number of trout affected by releases appears 

to be small. This view is supported by prior findings that 

indicate fewer than 6 percent of trout observations were in 

waters at least 1oC cooler than the river (fig. 25B), fewer than 

3 percent of trout observations were in waters cooler than 

20oC (fig. 28B), and only one of the five trout, occasionally 

observed in a thermal refuge, used it regularly (not shown). In 

the few cases where trout were in thermal refuges, increases 

in trout temperatures during releases were rare. Even though 

the releases did not appear to have biologically relevant effects 

on thermoregulatory behavior, brown trout in the Indian 

River probably grow slowly and have high mortality rates 

during summer months when they are thermally stressed for 

long periods. 

In the Hudson River, trout temperatures changed 

(either decreased or increased) rapidly in roughly 20 percent 

of observations on nonrelease days and in 59 percent of 

observations on release days (fig. 30B). The observations 

for nonrelease days serve as a baseline and show that trout 

behavior in the Hudson River is more variable than in the 

Indian River (and is unrelated to the releases); Hudson River 

trout moved into and out of refuge areas, sometimes warming 

and sometimes cooling, even when unaffected by the release 

bubble. On release days, trout temperatures increased in 

38 percent of observations and decreased in 22 percent of 

observations as the bubble passed through the study reach 

(fig. 30B). Increased temperatures indicate a dramatic 

reduction in thermoregulation (beyond the normal variability 

in behavior); however, decreased temperatures indicate that 

Figure 30. Graphs showing pPercentage (and number) of trout temperatures that increased, stayed the same, 

or decreased over the time span when release bubbles arrived at the trout’s location on nonrelease, release, and 

flooding days in the A, Indian River and B, Hudson River, Adirondack Mountains, New York, during 2006.

RELEASE

DAYS 

FLOODING

DAYS 

NONRELEASE

DAYS

100

80

60

40

20

0

100

80

60

40

20

0

PERCENTAGE OF TROUT TEMPERATURE OBSERVATIONS

= = =

10 8

2 15

5

2

2

7 13 12 4 22 6

B HUDSONRIVER

A INDIAN RIVER

=

EXPLANATION

Increase

No change

Decrease
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 63

individual trout were sometimes able to avoid the adverse 

effects of releases by moving into even cooler thermal refuges. 

It is possible that increased river stages during releases 

enhance access of trout to tributaries with shallow confluences. 

These findings—and earlier observations indicating fewer 

than 28.8 percent of trout were at least 1oC cooler than the 

river, fewer than 14.5 percent of trout were cooler than 20oC 

(table 24), and 5–7 out of 16–17 trout often used a thermal 

refuge (fig. 27)—collectively illustrate that thermal refuge 

habitat is much more available and (or) accessible to trout in 

the Hudson River than in the Indian River. 

Several observations suggest that the releases could be 

both detrimental and beneficial to brown trout in the Hudson 

River study reaches. In either case, the releases had a highly 

variable effect on trout in the Hudson; fewer trout were 

observed in thermal refuges during release days (23.5 percent) 

than during nonrelease days (27.3 percent) (fig. 25), and a 

greater percentage of trout exhibited temperature increases 

during release days (38 percent) than during nonrelease days 

(10 percent) (fig. 30B). These data indicate that stocked 

trout were using thermal refuges at low to moderate stages 

in the Hudson River, but that releases either decreased 

the amount and quality of thermal refuges or forced some 

trout from existing refuges. In contrast, temperatures of 

7 trout (22 percent of release-day observations) decreased 

during releases in the Hudson River (presumably when 

trout entered a cooler tributary), which indicates that the 

releases could actually have benefited study trout (not reduce 

thermoregulation) in some cases. These trout avoided dilution 

of thermal refuges during releases, possibly by moving into 

normally shallow refuges that were inaccessible except 

when river stages were augmented by releases. On the other 

hand, any disturbance to a thermally stressed trout, by itself, 

could adversely affect their growth and survival. Overall, 

time-span observations for a small number of trout in the 

Hudson River showed that releases affected thermoregulatory 

behavior; temperatures changed in 59 percent of trout during 

release days but in only 21 percent of trout during nonrelease 

days. These data indicate that the releases may have slightly 

increased thermal stresses for trout in the Hudson River. Since 

most brown trout in the Hudson River were exposed to such 

thermal stresses for extended periods, they likely grew more 

slowly and exhibited higher rates of mortality during the warm 

summer months (regardless of the releases) than they would 

have in a comparable but unregulated system such as the 

Cedar River. 

Movement Behavior—In 2006, about one-half of the 

15 study trout in the Indian River remained at the stocking 

location (a large deep pool), and most others dispersed 

downstream over a 4-km-long river segment during the 

first 24 hours (fig. 31B). After 1 week, the location pattern 

remained similar to that for the first 24 hours after stocking. 

At 1 month, trout were spread over a smaller range (about 

2.5 km), but many had moved upstream from the stocking 

location. Most trout occupied specific habitats: the stocking 

pool, a tributary 2 km downstream, a deep glide below rapids 

-6,000

-4,000

-2,000

0

2,000

4,000

6,000

-6,000

-4,000

-2,000

0

2,000

4,000

6,000

-6,000

-4,000

-2,000

0

2,000

4,000

6,000

DISTANCE FROM STOCKING LOCATION, IN METERS

C Hudson River

A Cedar River

B Indian River

Damlocation

Trout location

WEEKS AFTER STOCKING

0 1 2 3 4 5 6 7 8

EXPLANATION

Figure 31. Graphs showing dDispersal of individual brown trout 

upstream (positive) and downstream (negative) from stocking 

locations in the A, Cedar, B, Indian, and C, Hudson Rivers, 

Adirondack Mountains, New York, at approximately 1, 7, 30, and 

60 days after stocking during 2006.
64 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

(250 m upstream), and a deep pool at the base of rapids 

(500 m upstream). At 2 months, the only two persisting trout 

were in the stocking pool. No trout stocked into the Indian 

River were observed farther from the stocking area than the 

confluence of the Indian and Hudson Rivers; only 1 of the 

15 study trout was not accounted for.

All but 4 of the 15 trout stocked into the Hudson River 

during 2006 dispersed from the general area of the stocking 

location (the mouth of Raquette Brook , a cold water tributary) 

within 48 hours (fig. 31C). Roughly equal numbers of trout 

moved in upstream and downstream directions, spreading out 

over a 2.7-km-long river segment. At 1 week, the trout had 

dispersed farther upstream and downstream, spreading out 

over 10 km, with four trout remaining close to the stocking 

location. At 1 month, the seven persisting trout were spread 

over a 3-km-long river segment. At 2 months, the four 

persisting trout were spread over a 6.5-km-long river segment. 

Trout dispersal was highly variable in the Hudson River and 

did not display an obvious pattern. Several locations were 

regularly inhabited by study trout: two cold-water plumes, 

near the stocking tributary (Raquette Brook) and at Aldous 

Brook; and a deep pool downstream from the Boreas River. 

Most trout were observed singularly, however, the few 

observed aggregations consisted of pairs.

Mean dispersion (absolute distance upstream or 

downstream from the stocking location) varied among the 

three rivers and over time. Mean dispersion (±2SE) for trout 

in the Cedar River was 934 m (±409, n = 11) after the first 

day, 834 m (±409, n = 14) after the second week, 1,622 m 

(±681, n = 13) after 1 month, and 1,386 m (±716, n = 7) after 

2 months (fig. 32A). Trout in the Indian River were dispersed 

closer to the stocking location than they were in the other 

two rivers (fig. 32B). Dispersion in the Indian River averaged 

692 m (±610, n = 15) after 1 day, 815 m (±683, n = 14) 

after 1 week, 544 m (±445, n = 11) after 1 month, and 

80 m (±159, n = 2) after 2 months. Mean dispersion in the 

Hudson River was much narrower than in the Indian and 

Cedar Rivers after 1 day but much wider than in the other 

two rivers after 1 week (fig. 32C). Mean dispersion in the 

Hudson was 302 m (±163, n = 15) after 1 day, 1,535 m 

(±1064, n = 12) after 1 week, 703 m (±622, n = 7) after 

1 month, and 2,681 m (±1984, n = 4) after 2 months.

Lastly, median trout locations, the interquartile range 

(middle 50 percent) of locations, and the middle 95 percent of 

locations from all observations are shown in figure 33 for each 

river during 2006. In the Cedar River, the median location was 

just upstream of the Cedar River Dam and the fifth percentile 

was a pool at the base of the Cedar River Dam (fig. 33A). 

Although trout moved downstream from this dam, they often 

returned and remained at its base there for long periods of 

time. The middle 50 percent of locations was 1,911 m long 

and was skewed upstream from the median. The middle 

95 percent of locations was 2,193 m long (only slightly greater 

than the middle 50 percent) and similarly skewed upstream. 

In the Indian River, the median location was just downstream 

of the stocking pool (fig. 33B). The middle 50 percent of 

0

1,000

2,000

3,000

4,000

5,000

6,000

0

1,000

2,000

3,000

4,000

5,000

6,000

0

1,000

2,000

3,000

4,000

5,000

6,000

MEAN ABSOLUTE DISTANCE FROM STOCKING LOCATION, IN METERS

C Hudson River

A Cedar River

B Indian River

Mean distance

WEEKS AFTER STOCKING

0 1 2 3 4 5 6 7 8

EXPLANATION

+2X standard error

-2X standard error

Figure 32. Graphs showing mMean absolute distance 

(±2 × standard error) of all brown trout from the stocking 

locations in the A, Cedar, B, Indian, and C, Hudson Rivers, 

Adirondack Mountains, New York, at approximately 1, 7, 30, 

and 60 days after stocking during 2006.
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 65

C HUDSON RIVER

A CEDAR RIVER

B INDIAN RIVER

Stocking location

25th and 75th percentiles

5th and 95th percentiles

Dam location

Median

CedarRiverDam

Abanakee Dam

EXPLANATION

0

0 2 KILOMETERS

1

1

2 MILES

N

N

N

Hudson River

0 2,000 FEET

0

1,000

250 500METERS

0 2,000 FEET

0

1,000

250 500METERS

Browns Brook

Boreas River

Direction of streamflow

Thirte enth Bro o k

Brook

Deer Creek

Balm of Gilead

Griffin Brook

Aldous Brook

Raquette Brook

Black Hole

Figure 33. Maps showing dDistribution of brown-trout observations in generalized study reaches 

in the A, Cedar, B, Indian, and C, Hudson Rivers, Adirondack Mountains, New York, during 2006.
66 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

locations was only 120 m long and centered on the median. 

The middle 95 percent of locations was 2,838 m long and 

skewed downstream from the median. The median location in 

the Hudson River was also just downstream from the stocking 

tributary (fig. 33C). The middle 50 percent of locations was 

569 m long and skewed downstream from the median. The 

middle 95 percent of locations (6,059 m) was longer than 

in the other two rivers and heavily skewed upstream from 

the median.

Trout activity level, defined as the distance moved 

between consecutive days, can partly explain differences 

in trout distribution and dispersion among the three rivers. 

Daily activity levels of trout in the Indian River indicate 

that trout moved shorter (median = 15 m) distances than 

in the Hudson River and less variable distances than in 

both other rivers (fig. 34). Activity levels of trout were 

similarly low (median = 15 m) in the Cedar River and higher 

(median = 45 m) in the Hudson River than in the Indian 

River. Trout activity levels were significantly different among 

the three rivers (Kruskal-Wallis x2 = 29.0015, p = <0.0001). 

Results of Dunn’s tests (Zar, 1996) show trout activity in 

the Hudson River as significantly different from activity in 

the Cedar River (Q = 4.63) or the Indian River (Q = 5.11) 

at α = 0.05, although activity in the Indian River was not 

significantly different from that the Cedar River (Q = 0.74). 

Observations of trout locations made more than a day apart 

were not evaluated. In general, these findings indicate that 

trout moved more often (and farther) in the Hudson River 

than in either the Indian or Cedar Rivers. The metabolic cost 

of such movements would be high and could adversely affect 

growth and survival of stocked (and resident) trout because 

water temperatures in the Hudson River were near the upper 

critical range for brown trout (Elliot, 1994).

Persistence—Daily estimates of trout persistence 

(apparent survival) were determined by year and by river 

(fig. 35A–B) from July 25 to August 18 in 2005 and from 

June 14 to August 19 in 2006. During both years, trout in all 

rivers persisted for a minimum of 1 day and a maximum of 

24 days in 2005 and 72 days in 2006 (durations for tracking 

operations each year). Seventy-five percent of the trout in the 

Indian and the Hudson Rivers no longer persisted after 13 to 

20 days during 2005 (persistence in the Cedar River was not 

studied in 2005), whereas 75 percent of the trout in all rivers 

persisted at least 20 days during 2006. The middle 50 percent 

of persistence data for the Hudson and Indian Rivers showed 

similar trends between years, but trends varied considerably 

among the three rivers. Trout persisted in the Hudson River 

for the shortest time (median duration was 12 days in 2005 

and 23 days in 2006), somewhat longer in the Indian River 

(median duration was 16 days in 2005 and 36 days in 2006), 

and for the longest time in the Cedar River (median duration 

was 67 days in 2006). The median durations of persistence 

in Hudson and Indian Rivers did not differ significantly in 

2005 (x2 = 0.2312, p = 0.06306) or in 2006 (x2 = 0.9669, 

p = 0.3255). The median durations of persistence in the 

control, the Cedar River, differed significantly from values in 

the Hudson River (x2= 8.1059, p = 0.0044) and in the Indian 

River (x2 = 4.1176, p = 0.0424) during 2006. At the end of the 

2005 effort, only one trout remained in the Hudson River, and 

no trout remained in the Indian River. At the end of the 2006 

season, one trout remained in the Indian River, two remained 

in the Hudson River, and eight remained in the Cedar River. 

These observations indicate that average survival for stocked 

trout may be much lower in the Indian and Hudson Rivers 

than in the Cedar River (fig. 36). Given the limited physical 

habitat and stressful thermal conditions in the Indian River, 

low survival rates of stocked trout in this system could 

(hypothetically) be caused as much by the absence of thermal 

refuge areas as by the effects of flow releases. The percentage 

of trout using thermal refuges in the Hudson River was similar 

(when unaffected by releases) to that observed in the Cedar 

River; however, apparent trout survival in the Hudson River 

was poor and on a par with that in the Indian River. These 

results indicate that a combination of factors, such as poor 

physical habitat (for example, lack of deep slow water), low 

abundance of prey, or the releases affected trout mortality 

in the Hudson River. Collection of emaciated rainbow trout 

and brown trout (about 10 in. long) at two Indian River and 

Hudson River study sites during the summer of 2005 indicates 

that trout were generally unable to maintain their normal 

condition, even though anglers reported catching brook trout 

in the main-stem Cedar River and its tributaries. 

Final Location of Transmitters—The large number of 

transmitters confirmed or inferred to be in nearby woods or 

exposed in the flood zone indicates that predation may have 

been an important cause of trout mortality in all study reaches. 

Losing transmitters or their signals was not a problem in either 

the Cedar or Indian Rivers, but approximately one-third of the 

15 transmitters deployed in the Hudson River were lost during 

2005 and 2006 (fig. 37). Apparently, differences in valley 

slope, riparian communities, or other factors not addressed 

by this study contributed to the high rate of loss for trout and 

transmitters, mainly in Hudson River study reaches.
Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers 67

1

10

100

1,000

10,000

DAILY DISTANCE MOVED,

IN METERS

INDIAN

RIVER

HUDSON

RIVER

CEDAR

RIVER

Middle 50 percent of observations

Median

Range of observations

EXPLANATION

Figure 34. Graph showing sSummary of brown-trout activity (distance trout 

moved between consecutive days) in the Cedar, Indian, and Hudson Rivers, 

Adirondack Mountains, New York, during 2006.

0

5

10

15

20

25

30

0

10

20

30

40

50

60

70

80

PERSISTENCE OF TROUT, IN DAYS

A 2005

B 2006

INDIAN

RIVER

HUDSON

RIVER

CEDAR

RIVER

Middle 50 percent of observations

Median

Range of observations

EXPLANATION

INDIAN

RIVER

HUDSON

RIVER

Figure 35. Graphs showing pPersistence of brown trout (number of days trout 

were apparently alive and within the study reach) in the Cedar, Indian, and Hudson 

Rivers, Adirondack Mountains, New York, during A, 2005, and B, 2006.
68 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

16

14

12

10

8

6

4

2

June 14June 19June 24June 29

July 4July 9

July 14July 19July 24July 29

Aug. 3Aug. 8

Aug. 13Aug. 18

0

NUMBER OF TAGGED TROUT

DATE

2006

2006

2006

2005

2005

Cedar River

Indian River

Hudson River

Figure 36. Graph showing tThe number of tagged trout 

apparently alive each day and with the study reach in the Indian 

and Hudson Rivers during 2005 and 2006 and in the Cedar River 

during 2006, Adirondack Mountains, New York.

18

16

14

12

10

8

6

4

2

0

Cedar River

Hudson River

Indian River

NUMBER OF TRANSMITTERS

SIGNAL

LOST 

WOODS FLOOD

ZONE OR

SHALLOW

WATER

MIDCHANNELLIVING

FISH 

2005200620052006200520062005200620052006

Figure 37. Graph showing cConfirmed or inferred final 

location of transmitters that had been implanted into 75 brown 

trout and stocked into the Indian and Hudson Rivers during 

2005 and 2006 and into the Cedar River, Adirondack Mountains, 

New York, during 2006.
Summary 69

Summary

The water and biological resources in the lower Indian 

and upper Hudson Rivers were affected to different extents 

by the releases from Lake Abanakee. Some distinctive 

characteristics of these resources and measured or estimated 

effects that the releases may have on each are summarized by 

resource or by category below.

River Discharge and Stage

• Discharge at the Indian River below Lake Abanakee 

(IR01) increased on average by 1,207 ft3/s during 

releases from June to September 2005 and by 

1,410 ft3/s from June to September 2006. 

• Mean monthly increases in river stage during releases 

ranged from 0.79 to 2.14 ft at the three Indian River 

sites and from 0.67 to 3.15 ft at the four Hudson River 

sites downstream from the dam during June, July, 

August, and September of 2005 and 2006.

• River stage and flow in the Indian River below Lake 

Abanakee usually decreased after gate closure to levels 

lower than before the gate was opened, and they did 

not recover to prerelease levels roughly half of the time 

before the next release cycle began.

River Temperatures

• The recreational flow releases caused no significant 

or biologically relevant change in water temperatures 

at all fixed study sites in the Indian and the 

Hudson Rivers.

• Independently of releases, water temperatures at all 

study sites commonly exceeded the threshold (20oC) 

known to be stressful to brown trout. 

• Mean and median water temperatures on release days 

were slightly lower than mean and median water 

temperatures on nonrelease days.

Lake Stage (Surface-Water Elevation) in 

Lake Abanakee

• The releases caused Lake Abanakee stage to 

consistently decrease by about 0.3 ft on release days 

during June to September of 2005 and 2006.

• In 2005, lake stage fully rebounded between 

successive releases 50 percent of the time; recovery 

before the next release averaged 91 percent of the 

prerelease stage.

• In 2006, lake stage fully rebounded between 

successive releases 58 percent of the time; recovery 

before the next release averaged 98 percent of the 

prerelease stage.

Stream Habitat 

• Short riffles dominated habitat at most Indian River and 

Hudson River study sites during base flows, and fewer 

but larger habitat units were evident during releases.

• Increased water velocities dramatically increased the 

amount of fast-water habitat (rapid, riffle, run) during 

releases. The releases also decreased the amount 

of slow-water habitat (pool, glide, backwater, side 

channel) in all study reaches.

Wetlands

• Surveyed shorelines of the Indian River contained 

fewer wetlands than did control reaches in the 

Cedar River.

• Although differences in the extent of wetlands 

bordering the Indian and Cedar Rivers may be 

attributed in part to the releases, both positive and 

negative effects on wetlands are conceivable and 

indicate that more research is needed to assess the 

net effect.

Temporal and Spatial Patterns in River 

Temperatures

• Few individual thermal refuges (waters at least 1oC 

lower than the main channel) were evident in the 

27-km study reach during normal summer base flows.

• Five cold-water tributaries that enter the Hudson River 

downstream from its confluence with the Boreas 

River provided most of the near-bank and off-channel 

thermal refuge areas in the study reach.

• The high-flow bubble produced by the releases from 

Lake Abanakee essentially eliminated all main-channel 

refuges by swamping inputs from the five coldwater tributaries.

• Analysis of temperature patterns at different spatial 

scales offers conflicting evidence of the effects 

on quality of fish habitat. Water temperatures in 

the middle of the reach (at Hudson Gorge) were 

consistently lower than those in the upper and lower 

reaches, and the high-flow bubble did not diminish the 

cooling effect. 
70 Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York, 2004–06

• Remote imaging is an effective technique for 

identifying and characterizing certain cold-water 

(thermal) refuges in streams, but analyses and results 

can sometimes be limited by its inability to accurately 

separate water data from land-surface data or to detect 

seeps on the river bottom.

Fish Assemblages

• Fish-community biomass, density, and richness in the 

Indian River were strongly affected by releases at the 

first site below Lake Abanakee (IR01); these indexes 

were moderately affected at the two other sites (IR02 

and IR03). Releases had a slight effect on community 

indexes at the first Hudson River site below its 

confluence with the Indian River (HR02); the effects 

of releases on community indexes at sites HR04 and 

HR05 were either positive or nonexistent.

• Releases had a strong effect on density of individual 

fish populations at all Indian River sites but the effects 

were less obvious, nonexistent, or contrary to those 

expected in the Hudson River.

• Releases severely affected the total biomass of 

populations of dominant species only at the first site 

downstream from Lake Abanakee (IR01). The total 

biomass of species populations at Hudson River study 

sites reflected the addition of several species, small or 

no decreases in the number of species, and a general 

increase in the balance of species populations at 

sites farther downstream; these trends appeared to be 

unrelated to the releases.

• There is no way to prove that other unmeasured 

factors did not contribute to the differences noted 

among fish communities at study sites in all three 

rivers. More precise information on fish communities, 

hydrology, and habitat would be needed to completely 

document site-to-site similarities and differences and 

determine whether the releases alone caused observed 

differences in population and community indexes, or 

whether some combination of physical, chemical, and 

biological factors caused them.

Macroinvertebrate Communities

• Macroinvertebrate community indexes indicate that 

the recreational-flow releases did not contribute 

substantially to the effects of the continuous releases of 

impounded waters from Lake Abanakee into the Indian 

River, and that any impoundment effect did not extend 

to study sites in the Hudson River. 

• The larger percentage of scrapers at CR01 than at IR01, 

IR02, and IR03, and the occurrence of two collectorfilterer species only at IR01, indicate that the releases 

had a minor effect on macroinvertebrate assemblages 

in the Indian River, primarily in the reach closest to the 

Lake Abanakee Dam. Comparable changes in feeding 

guilds or in dominant species were not evident at any 

Hudson River study site.

Trout Telemetry

• Use of thermal refuges by stocked brown trout varied 

among study reaches and ranged from low to moderate 

levels in the three rivers.

• The releases generally decreased the ability of many of 

the trout that were using thermal refuges in the Indian 

and Hudson Rivers to continue using them.

• Brown trout near tributaries in the Hudson River 

occasionally maintained lower temperatures than the 

river or moved into cooler tributary waters to avoid 

negative effects of releases.

• Multilevel effect analyses indicate the releases 

had a statistically significant negative effect on 

thermoregulation of study trout in the Indian and 

Hudson Rivers.

• Releases increased average temperatures of brown 

trout by 0.5°C in the Indian River and by 1.0°C in the 

Hudson River; however, the biological significance of 

their reduced ability to thermoregulate is uncertain.

• Daily movement of trout was significantly greater 

in study reaches of the Hudson River than in either 

the Indian or the Cedar Rivers, and movement was 

generally unaffected by the releases in the Indian and 

Hudson Rivers.

• Apparent survival for stocked trout was very low and 

similar in the Indian and Hudson Rivers during 2005 

and 2006, but survival was higher in the Cedar River 

than in the other two rivers during 2006.
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Baldigo and others—Effects of Recreational Flow Releases on Natural Resources of the Indian and Hudson Rivers, New York—Scientific Investigations Report 2010–5223