Prepared in cooperation with the St. Regis Mohawk Tribe-Environment Division

Dam Removal, Connectivity, and Aquatic Resources 

in the St. Regis River Watershed, New York

Scientific Investigations 2015–5116

U.S. Department of the Interior

U.S. Geological Survey
Cover photograph. USGS Aquatic Ecology Technician, Emma Mrowka; Mohawk Tribe Water 

Quality Technician, Dylan Herne; and Fish and Wildlife Technician, Jay Wilkins. This photo was 

provided by the St. Regis Mohawk Tribe-Environmental Division. 
Dam Removal, Connectivity, and 

Aquatic Resources in the St. Regis River 

Watershed, New York

By James E. McKenna, Jr., Kaitlin Hanak, Katharine DeVilbiss, Anthony David, 

and James H. Johnson

Prepared in cooperation with the St. Regis Mohawk Tribe-Environment Division

Scientific Investigations Report 2015–5116

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2015

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Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

McKenna, J.E., Jr.; Hanak, Kaitlin; DeVilbiss, Katharine; David, Anthony; and Johnson, J.H., 2015, Dam removal, 

connectivity, and aquatic resources in the St. Regis River watershed, New York: U.S. Geological Survey Scientific 

Investigations Report 2015–5116, 15 p., http://dx.doi.org/10.3133/sir20155116.

ISSN 2328-0328 (online)
iii

Acknowledgments

This study was conducted in cooperation with the St. Regis Mohawk Tribe (SRMT)-Environment 

Division. The authors thank the members of the SRMT, as well as Emma Mrowka, for assistance 

with field collections. The authors also thank Robert Alexander and Michael Slattery for their 

assistance with geographic information system data and Heather Galbraith for her assistance 

with native mussel identification. Lastly, the authors thank the private land owners in the study 

area for their cooperation. This research was funded by the U.S. Geological Survey (USGS)-

Ecosystem Program. Substantial support was provided by the USGS-Great Lakes Regional 

Aquatic Gap Analysis Project.

v

Contents

Acknowledgments........................................................................................................................................iii

Contents...........................................................................................................................................................v

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

Introduction.....................................................................................................................................................1

Methods...........................................................................................................................................................2

Results .............................................................................................................................................................4

Near-Dam Conditions...........................................................................................................................4

Measuring the Effects of Dam Removal ...........................................................................................7

Headwater Conditions .........................................................................................................................7

Connectivity Assessment ..................................................................................................................11

Summary and Conclusions.........................................................................................................................11

Limitations............................................................................................................................................12

Future Research Needs.....................................................................................................................13

References Cited..........................................................................................................................................13

Appendix 1. Fish Species Code Definitions..........................................................................................15

Figures

1. Map showing St. Regis subwatersheds, observed and U.S. Geological 

Survey-Great Lakes Regional Aquatic Gap Analysis Project (GLGap) 

predicted suitability of Brook Trout habitat, and actual Brook Trout 

abundance at labeled sample sites...........................................................................................3

2. Map showing sites sampled and predicted water levels in the reservoir 

following removal of the Hogansburg Dam, Franklin County, New York .............................5

3. Vertical graph of species assemblage based on sample sites near the 

Hogansburg Dam, Franklin County, New York .........................................................................6

4. Graph showing habitat characteristics affecting Brook Trout abundance 

near Hogansburg Dam, Franklin County, New York ................................................................9

Tables

1. Species richness of sample site catches near Hogansburg Dam, 

Franklin County, New York...........................................................................................................6

2. Estimated surface areas, volumes of water, and exposed reservoir bed 

above the Hogansburg Dam, Franklin County, New York.......................................................7

3. Sampling efficiency for 1-pass electrofishing for sufficiently calculating 

species abundance near Hogansburg Dam, Franklin County, New York............................8

4. Fish catch per unit effort (CPUE; standardized abundance in units of fish 

100 square meters), species richness (number of species present), species 

diversity (Shannon-Weaver information index; Shannon and Weaver, 1949), 

and evenness (index of the distribution of total abundance among species 

present) of fish assemblages in headwater sites near Hogansburg Dam, Franklin 

County, New York..........................................................................................................................8

5. Multiple linear regression of Brook Trout abundance as a function of altitude, 

water temperature, and stream size .......................................................................................11
vi

Conversion Factors

International System of Units to Inch/Pound

Multiply By To obtain

Length

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

kilometer (km) 0.5400 mile, nautical (nmi) 

meter (m) 1.094 yard (yd) 

Area

square meter (m2

) 0.0002471 acre 

square kilometer (km2

) 247.1 acre

square meter (m2

) 10.76 square foot (ft2) 

square kilometer (km2

) 0.3861 square mile (mi2)

Volume

cubic meter (m3

) 264.2 gallon (gal) 

cubic meter (m3

) 0.0002642 million gallons (Mgal) 

cubic meter (m3

) 35.31 cubic foot (ft3)

cubic meter (m3

) 1.308 cubic yard (yd3) 

cubic kilometer (km3

) 0.2399 cubic mile (mi3) 

cubic meter (m3

) 0.0008107 acre-foot (acre-ft) 

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

°F = (1.8 × °C) + 32.

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

°C = (°F – 32) / 1.8.

Datum

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

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

Altitude, as used in this report, refers to distance above the vertical datum.

Supplemental Information

Specific conductance is given in microsiemens per centimeter at 25 degrees Celsius (μS/cm at 

25 °C).

Concentrations of chemical constituents in water are given in milligrams per liter (mg/L).
vii

Abbreviations

Chl-a chlorophyll a

CPUE catch per unit effort

DF degrees of freedom

DO dissolved oxygen

F analysis of variance T statistic

FEMRF Fish Enhancement, Mitigation, and Research Fund

FERC Federal Energy Regulatory Commission

GAP USGS National GAP Analysis Program

GIS geographic information system

GLGap USGS Great Lakes Regional Aquatic Gap Analysis Program

GPP generator powered pulsator

GPS global positioning system

ORP oxidation reduction potential

ppm parts per million

SRMT St. Regis Mohawk Tribe

USGS U.S. Geological Survey

Dam Removal, Connectivity, and Aquatic Resources 

in the St. Regis River Watershed, New York

By James E. McKenna, Jr.,1 Kaitlin Hanak,1 Katharine DeVilbiss,1 Anthony David,2 and James H. Johnson1

1

U.S. Geological Survey

2

St. Regis Mohawk Tribe-Environment Division

Abstract

The decommissioning and planned removal of the 

Hogansburg Dam on the St. Regis River in New York has 

stimulated interest in the potential effects of that barrier 

removal on the St. Regis watershed. There will be immediate 

and systemic effects of the Hogansburg Dam removal, 

which may include inundation of habitats below the dam or 

dewatering of habitats above the dam, possibly affecting local 

fish assemblages and (or) local native mussel assemblages; 

and expansion of stream network connectivity, which has the 

potential to open a large area of the watershed to migratory 

aquatic species. Information was collected about biota, water 

quality, sediment distribution, riverbed dimensions in the 

vicinity of the dam, and habitat characteristics of headwater 

sample sites. Complete fish assemblages were collected, but 

species of special concern associated with the connectivity 

changes included, American Eel, Atlantic Salmon, Brook 

Trout, Eastern Sand Darter, and Lake Sturgeon. Freshwater 

mussels in the vicinity of the dam also were examined and 

may be at risk of exposure (without a rescue plan) after dam 

removal. Reservoir sediment will be transported downstream 

and will alter aquatic habitat as it moves through the system. 

The dam removal will open more than 440 kilometers of 

stream habitat to migratory species, allowing them to more 

easily complete their life cycles. Fish assemblages above the 

dam may be altered by migrating fishes, but resident Brook 

Trout are not expected to be adversely affected.

Introduction

Thousands of human-made dams exist within U.S. waterways, and most impede or prevent movement of fish and other 

aquatic organisms within and among watersheds and their 

components (McLaughlin and others 2013). Their presence 

also alters natural hydrology and can affect other aspects of 

lotic systems (Bednarek 2001; Hart and others 2002). Many 

of these barriers no longer serve the purpose for which they 

were constructed (Wildman 2013). Dam removal can alleviate 

the fish passage problem, but also can cause problems. The 

decommissioning and planned removal of the Hogansburg 

Dam on the St. Regis River in New York has stimulated 

interest in the potential effects of that barrier removal on 

the St. Regis watershed. The Hogansburg Dam is part of the 

485 kilowatt Hogansburg Hydroelectric project, operated by 

Erie Boulevard Hydropower. The first Federal Energy Regulatory Commission (FERC) license to operate the dam was 

issued in October 1985, and the current license expires in 

September 2015. Built in 1930, the spillway is 75 meters (m) 

wide by 3.5 m high (Erie Boulevard Hydropower, written 

commun., 2012b). The dam is located near the mouth of the 

river and is a barrier to fish movement in this relatively large 

watershed (2,217 square kilometers [km2

]) that drains a portion of the Adirondack Mountains down to the St. Lawrence 

River. Ecologic and hydrologic conditions in the immediate 

vicinity of the Hogansburg Dam and in headwater habitats of 

the St. Regis watershed were examined, with a focus on access 

for migratory American Eel (Anguilla rostrata) and Atlantic 

Salmon (Salmo salar), drainage network connectivity to native 

Brook Trout (Salvelinus fontinalis) habitats, and potential 

effects of dam removal on threatened Eastern Sand Darters 

(Ammocrypta pellucida) and freshwater mussels. 

This project was conducted by the U.S. Geological 

Survey (USGS), in cooperation with the St. Regis Mohawk 

Tribe (SRMT). The SRMT is interested in removal of the dam 

to enhance and rehabilitate the natural aquatic (and wetland) 

resources of their reservation and adjacent areas. Decommissioning and removal of the dam will repatriate lands within the 

project boundary back to the SRMT. Associated research on 

the St. Regis River watershed—as part of the Fish Enhancement, Mitigation, and Research Fund (FEMRF)—funded 

the effort to identify threatened and endangered fish species 

and characterize their habitats within the St. Lawrence River 

Valley and substantially augments the data and findings of 

this study (J.E. McKenna, U.S. Geological Survey, written 

commun., 2012). Also, products of the USGS Great Lakes 

Regional Aquatic Gap Analysis Project (GLGap) (McKenna 

and others, 2014), especially the Brook Trout species distribution model (McKenna and Johnson, 2011), aided with sampling design for this study and will benefit from the additional 

validation data provided by this study. 
2 Dam Removal, Connectivity, and Aquatic Resources in the St. Regis River Watershed, New York

The two major aspects of this project are the immediate 

and systemic effects of the Hogansburg Dam removal, which 

may include inundation of habitats below the dam or dewatering of habitats above the dam, possibly affecting local fish 

assemblages and (or) local native mussel assemblages (Stanley 

and others, 2002; Cooper 2011); and expansion of stream network connectivity, which has the potential to open a large area 

of the watershed to migratory aquatic species. Information 

was collected about biota, water quality, sediment distribution, 

riverbed dimensions in the vicinity of the dam, and habitat 

characteristics of headwater sample sites.

There were several species of special concern associated with the connectivity changes. American Eel is declining 

throughout its native range, including in the St. Lawrence 

River system above the Beauharnois Dam in Quebec, Canada 

(D.E. Dittman, U.S. Geological Survey, written commun., 

2010). American Eel are catadromous (migrating between 

fresh and salt water as part of their life cycle), long-range 

migrants with extreme abilities to migrate upstream and over 

or around most small to moderate-sized natural (and many 

man-made) barriers, and occupy nearly every aquatic habitat 

within a watershed. Despite this impressive migratory ability, each major barrier affects their ability to move upstream 

and represents a potential cause of mortality. Removal of the 

Hogansburg Dam would improve American Eel migratory 

access to the St. Regis watershed. 

Atlantic Salmon is thought to have been native to the 

St. Regis and other watersheds draining into the St. Lawrence 

River (Goodyear and others, 1982). The SRMT name for the 

hamlet of Helena, New York, located on the St. Regis River 

(8.2 kilometers [km] upstream of the of the Hogansburg Dam 

spillway), is Ohiekarónth:ne or “the place of the salmon,” 

suggesting a historical location for the SRMT salmon harvest. Small-scale reintroductions of Atlantic Salmon into the 

St. Regis River and adjacent Little Salmon River watershed 

have shown that this species will persist in the system and 

attempt spawning migrations into the St. Regis watershed. 

Dam removal will make spawning habitat accessible to Atlantic Salmon, potentially allowing completion of the natural life 

cycle. 

While the large increase in the stream network accessible 

to migratory species is generally considered an ecological 

improvement, there are possible negative effects for headwaters species presently isolated by the dam. Native Brook Trout 

occur in the headwaters of the St. Regis watershed, and separate populations are likely. If among these populations there is 

a strain that is strongly migratory, then access to the St. Lawrence River will allow for a complete migratory cycle. Overwintering Brook Trout are known to move 65–100 km from 

large rivers to upstream habitats (Curry and others, 2002); 

however, native resident Brook Trout may be affected by the 

dam removal through exposure to migratory fish species that 

have not previously had access to a large portion of the stream 

network (Stanley and Doyle, 2003). For example, although the 

parasitic Sea Lamprey (Petromyzon marinus) is not considered 

a significant problem in this part of the St. Lawrence River 

Valley, expanded access to the St. Regis watershed could make 

more spawning and nursery habitat available to Sea Lamprey 

(McLaughlin and others, 2013). Other species like Walleye 

(Sander vitreus) and Lake Sturgeon (Acipenser fulvescens) 

would also likely benefit from the expanded access to this 

watershed (D.E. Dittman, U.S. Geological Survey, written 

commun., 2009; Landsman and others, 2011). 

Methods

The sampling design and sample collection and analysis 

methods were similar to those used in the FEMRF study 

(J.E. McKenna, U.S. Geological Survey, written commun., 

2012). The main stem and tributary habitats within 1 km of 

the Hogansburg Dam were sampled with seine, backpack, and 

boat electroshockers, and gillnets.

The Brook Trout species distribution model, developed 

for New York State by the GLGap (McKenna and others, 

2015), was used to help stratify headwater sampling sites. This 

model predicts Brook Trout abundance potentially supported 

by the habitat in each stream segment of the St. Regis watershed. These predictions were used in conjunction with field 

observations to classify headwater streams into quality categories. In the field, the quality of these streams was assessed 

by substrate type, water flow, measured water temperature, 

and depth for feasibility of backpack electrofishing. Stream 

section categories for fish sampling were predicted by GLGap 

analysis models to be high-quality sites (11–100 Brook Trout 

per 100 square meters [m2

]) and, upon field assessment, 

judged as highly suitable habitat; those predicted to be low 

quality (0–10 Brook Trout per 100 m2) but field judged as 

highly suitable habitat; and those predicted to be high quality 

but field judged to be poor quality Brook Trout habitat. Five 

stream reaches from each of the previously mentioned quality 

categories were selected for backpack electroshock sampling. 

The GLGap hydrospatial framework (McKenna and others, 

2015) was used to identify distinct major stream network units 

(subwatersheds) to ensure representativeness of the sampling 

design. The GLGap subwatersheds divided the St. Regis 

watershed into six subwatersheds; headwaters in three of these 

units were sampled (fig. 1). In addition, the SRMT-FEMRF 

work contained samples from the lowest subwatershed, as 

well as the lower portion of two subwatersheds covered by the 

headwaters work in this study.

These and other sites were evaluated for their connectivity to the watershed stream network. The dam and waterfalls 

database available for New York (D.E. Dittman, U.S. Geological Survey, written commun., 2010) was used in a geographic 

information system (GIS) to enumerate the number of known 

barriers below the headwater sites. Field assessment included 

documentation of natural (waterfalls and beaver dams) and artificial (dams and culverts) barriers. Changes in the connectivity 

and potential increase in accessible habitat for migratory fish 

resulting from dam removal also was evaluated with the GIS.
ST-E112

ST-E111

ST-E110

ST-E109

ST-E108 ST-E107

ST-E106

ST-E105

ST-E104

ST-E103

ST-E102

ST-E101

ST-E100

Helena

74°40' 74°20' 74°

45°

44°50'

44°40'

44°30'

75° 74°40' 74°20' 

0 5 10 15 Miles

0 5 10 15 Kilometers

Base from U.S. Geological Survey, 2002. National Hydrography Data, 1:100,000. Coordinate System: Albers Equal Area Conic USGS CONUS NAD83. Projection: Albers. Datum: North American Datum of 1983 (NAD 83).

False Easting: 0.0000. False Northing: 0.000Standard Parallel 1: 29.5000. Standard ParaLatitude Of Origin: 23.0000. Units: Meter.

GLGap predicted  per 100 square Actual Brook Trou

Assessed/predict suitability

Hogansburg Dam

Barrier to conduc

Culvert

St. Regis subwate

EXPLANATI

Lower St. RegisSt. RegisDeer RiverBartonSantimawWest Branch St. 

NEW YORK

PENNSYLVANIA

LAKE ONTAR IO

02−1011−100More than 100High/suitableHigh/unsuitableLow/suitableLow/unsuitable

01−10

11−100

Figure 1. The St. Regis subwatersheds, observed and U.S. Geological Survey-Great Lakes Regional Aquatic Gap Analysis Project (GLGap) prBrook Trout habitat, and actual Brook Trout abundance at labeled sample sites.
4 Dam Removal, Connectivity, and Aquatic Resources in the St. Regis River Watershed, New York

Headwater fish assemblages were assessed using a singlepass, backpack-electrofishing technique within a 50 m reach, 

adjusted for sampling efficiency. Multi-pass elimination 

(removing fish by electroshocking multiple times throughout 

the same stream reach) was used at two headwater sites to 

estimate single-pass catch efficiencies for Brook Trout and 

several other species (Peterson and others, 2004). Efficiency 

values were then used to more accurately estimate the population of fish at a site based on the number of fish captured. 

Standardized abundance, catch per unit effort (CPUE), was 

calculated as the number of fish captured divided by the area 

sampled for each site and divided by the efficiency for each 

species to estimate fish per 100 m2. The location of each 

sample site was recorded with a handheld global positioning 

system (GPS) (Garmin GPSmap 60CS), and the local habitat 

was characterized by measurement of water temperature, 

specific conductance, oxidation reduction potential (ORP), 

pH, dissolved oxygen, turbidity, and chlorophyll a. Stream 

width, maximum depth, and flow were recorded every 

10 m within the 50 m sample reach. The association of Brook 

Trout abundance with fine-scale (on-site) habitat conditions 

was examined using linear regression. Fish assemblage 

diversity was represented by richness (the number of species), 

evenness (the partitioning of total abundance by species), and 

diversity as measured by the Shannon-Weaver Information 

Index (Shannon and Weaver, 1949). These are common metrics that describe multispecies communities.

Samples of the conditions in the immediate vicinity of 

the dam were collected in a number of ways. One seine collection using a hybrid 9.1 m long (1/4-inch (in.) mesh wings 

and 1/8-in. mesh bag) (McKenna and others, 2013) was used 

in sandy habitat below the dam during this study. In addition, 

the FEMRF project (J.E. McKenna, U.S. Geological Survey, 

written commun., 2012) provided the following samples from 

the previous 2 years: 

• one seine sample in soft sediment above the dam, 

• one backpack shocking sample made in the lowest 

reach of a tributary entering the river below the dam, 

• one boat electrofishing sample (using a Smith-Root kit 

7.5 generator-powered pulsator on a 20-foot Crestliner 

C 2070 with umbrella cathodes, yielding a 60-cycle 

alternating current operating at 40 percent, with output 

normally at 9 amperes) made in the reservoir above the 

dam, and 

• seven gillnet samples (1–3-in. paneled monofilament 

mesh, 38 m in length, 1.8 m in height), two above the 

dam, and three below the dam. 

The freshwater mussel community was qualitatively 

assessed by visual survey along the shore above the dam 

(particularly at a known muskrat midden) and by snorkeling 

both above and below the dam.

We also conducted a bathymetric survey using side-scan 

sonar (Hummingbird 997C Side-scan sonar unit) to document 

important characteristics of the riverbed above and below the 

dam. The transect above the dam started just above the safety 

buoys and extended upstream to the head of the reservoir. The 

volume of water in the reservoir was estimated by using a map 

of the area imported into ArcGIS and applying the three-dimensional analysis tool to create a surface of the reservoir bottom; 

assuming that there was a steep bank extending to 0.7 m on 

each side of the reservoir and that the bottom then sloped gently 

to the nearest set of side-scan sonar measurements. Side-scan 

depth measurements were augmented by data provided in a 

previous sediment survey report (Erie Boulevard Hydropower, 

written commun., 2012b). The full volume of the reservoir (on 

the day the bathymetric survey was conducted) was estimated, 

as well as the volume remaining after dam removal, assuming resultant water depth of 1.0 m or 0.5 m (depths typical of 

the areas above the reservoir). The exposed reservoir bottom 

resulting from the drawdown after dam removal was estimated 

by the difference in surface areas of the full reservoir and that 

of the surface area at 1.0 m water depth or 0.5 m water depth.

Results

Near-Dam Conditions

In the immediate vicinity of the dam, a total of 26 fish species were collected at 11 sample sites (fig. 2, table 1). Sample 

species richness ranged from 2 to 11, with a seine collection 

above the dam (ST-S007) being the richest. Gillnet and boat 

electrofishing samples represent the deepwater component of 

the fish community. The boat electrofishing sample above the 

dam (ST-B001) was dominated by Smallmouth Bass (Micropterus dolomieu) and Brown Bullhead (Ameiurus nebulosus) 

with lesser abundances of Northern Pike (Esox Lucius), Rock 

Bass (Ambloplites rupestris), Silver Redhorse (Moxostoma 

anisurum), and Walleye (fig. 3). Seines represent the shallow water component of the community in the main stem, and 

the assemblages above and below the dam were quite different. However, there was only a single seine sample from just 

upstream and downstream of the dam. That component above 

the dam (site ST-S007) was dominated by Rosyface Shiner 

(Notropis rubellus) and Common Shiner (Luxilus cornutus) 

with lesser abundances of other minnows and a few centrarchids 

(sunfish and bass), while the assemblage below the dam (site 

ST-S100) was strongly dominated by Mimic Shiner (Notropis 

volucellus), with all remaining species being darters, including 

Eastern Sand Darter. The seine collection (ST-S100) below the 

Hogansburg Dam was over mostly sand substrate (95 percent) 

located on the downstream side of the island approximately 

400 m below the dam. Six Eastern Sand Darters—a New York 

State Threatened Species—were caught, along with 108 Mimic 

Shiners, 1 Tessellated Darter (Etheostoma olmstedi), 1 Johnny 

Darter (Etheostoma nigrum), and 4 Channel Darter (Percina 

copelandi). 
Methods 5

EXPLANATION

Hogansburg Dam

Impoundment head

Mussel search sites

Gillnetting sample

Seine sample

Boat electroshocking sample

Backpack electroshocking sample

Water level 0.5 meter above bottom

Water level 1.0 meter above bottom

Current water level

Coordinate System: USA Contiguous Albers Equal Area Conic USGS version. Projection: Albers. 

Datum: North American Datum of 1983 (NAD 83). False Easting: 0.0000. False Northing: 0.0000. 

Central Meridian: -96.0000. Standard Parallel 1: 29.5000. Standard Parallel 2: 45.5000.

Latitude Of Origin: 23.0000. Units: Meter.

ST-G008

ST-G011

ST-G010 ST-G009

ST-G002

ST-G016

ST-G001

ST-S100

ST-S007

ST-B001

ST-E005

74°40' 74°39'45" 74°39'30"

44°58'45"

44°58'30"

44°58'15"

44°58'

74°40'15" 74°40' 74°39'45"

44°58'30"

44°58'15"

0 250 500 750 1,000 FEET

0 100 200 300 METERS

Source: Esri, DigitalGlobe, GeoEye, i-cubed, Earthstar Geographics,CNES/Airbus DS, 

USGS, AEX, Getmapping, Aerogrid, IGN, IGP, swisstopo,and the GIS User Community.

Hogansburg

Dam

NEW YORK

PENNSYLVANIA

LAKE ONTAR IO

Figure 2. Sites sampled and predicted water levels in the reservoir following removal of the Hogansburg Dam, Franklin County, 

New York. (Collection equipment used is indicated by different color circles, and sites are labeled with assigned site code.) 
6 Dam Removal, Connectivity, and Aquatic Resources in the St. Regis River Watershed, New York

Table 1. Species richness of sample site catches near Hogansburg Dam, 

Franklin County, New York.

Site code Collection 

equipment type

Species 

richness

Relative location 

from dam

ST-B001 Boat electrofisher 6 Above

ST-G001 Gillnet 4 Above

ST-G002 Gillnet 2 Above

ST-G016 Gillnet 2 Above

ST-S007 Seine 11 Above

ST-E005 Backpack electrofisher 8 Below

ST-G008 Gillnet 2 Below

ST-G009 Gillnet 5 Below

ST-G010 Gillnet 4 Below

ST-G011 Gillnet 4 Below

ST-S100 Seine 5 Below

Johnny Darter

Bluegill

White Sucker

Bluntnose Minnow

Muskellunge

Finescale Dace

Channel Darter

Golden Shiner

Pumpkinseed

Eastern Sand Darter

Northern Pike

Longnose Gar

Channel Catfish

Tessellated Darter

Spotfin Shiner

Central Mudminnow

Fallfish

Yellow Perch

Brown Bullhead

Common Shiner

Walleye

Fantail Darter

Rockbass

Rosyface Shiner

Fathead Minnow

Silver Redhorse

EXPLANATION

0

10

20

30

40

50

60

70

80

90

100

Gillnet sample 

above dam

Gillnet sample 

below dam

Seine sample

above dam

Backpack

electrofishing sample

on tributary below dam

Boat 

electrofishing sample

Assemblage composition, in percent

Seine sample

below dam

above dam

Figure 3. Species assemblage based on sample sites near the Hogansburg Dam, Franklin County, New York. (See fig. 2 for site 

locations; see appendix 1 for complete species list.)
Results 7

One backpack electroshocking site (ST-E005) sampled in 

a tributary below the dam contained Fathead Minnow (Pimephales promelas), Fantail Darter (Etheostoma flabellare), and 

Central Mudminnow (Umbra limi), as well as Tessellated 

Darter, Fallfish (Semotilus corporalis), Finescale Dace (Chrosomus neogaeus), Yellow Perch (Perca flavescens), and Pumpkinseed (Lepomis gibbosus) in lower numbers. Only gillnet 

collections provided multiple samples above (sites ST-G001, 

G002, and G016) and below the dam (sites ST-G008, G009, 

G010, and G011); this community component in both areas 

was dominated by Smallmouth Bass and Silver Redhorse with 

moderate abundances of Walleye. Rock Bass and Fallfish were 

only abundant above the dam; Yellow Perch, Longnose Gar 

(Lepisosteus osseus), and Channel Catfish (Ictalurus punctatus) were found only below the dam.

Visual walking and snorkel searches for freshwater mussels were conducted approximately 400 m above and below 

the Hogansburg Dam. We found old shell remains and (or) 

live specimens of Eastern Elliptio (Elliptio complanata) and 

Yellow Lamp Mussel (Lampsilis cariosa). Mussels were found 

in a fairly dense bed above the dam, but they were scattered 

below the dam. Shells were particularly abundant at a muskrat 

midden 400 m above the dam. 

Measuring the Effects of Dam Removal

The side-scan sonar survey covered an area of 0.87 km2

above the dam (table 2) and provided a map of the water depth 

and sediment composition within the reservoir. Results indicate that a range of approximately 117,000 to 145,000 cubic 

meters (m3) of water will discharge downstream when the dam 

is removed, and 32 to 50 percent of the reservoir bed will be 

dewatered (fig. 2). The bathymetric survey was insufficient to 

characterize the types of sediment present or to estimate the 

volume of sediment above the dam. However, in 2012, a sediment characterization study was performed by Erie Boulevard 

Hydropower, L.P, above the Hogansburg Hydroelectric Project 

(Erie Boulevard Hydropower, written commun., 2012b). 

That study determined that the riverbed generally consisted 

of gravel and boulders with minimal finer sediment accumulation, and the shorelines consisted of soft clays and silts. 

Sediment probes determined the sediment depth ranged from 

0.0 to 1.9 m, with greater depths along the shoreline and shallower depths in the head of the reservoir. The sediment depth 

changes from uniform and shallow, to irregular and deep, 

moving from the dam to the head of the reservoir. The majority of stored sediment likely will be transported downstream 

during dewatering.

Headwater Conditions

Sample sites were located in three of the six subwatersheds within the St. Regis watershed (sites ST-E100–113 on 

fig. 1). Accessibility to headwater habitats varied among the 

subwatershed units. Access to stream reaches within the subwatershed containing the West Branch, as well as a large portion of the main stem subwatershed, was limited by extensive 

tracts of private property where permission to enter could not 

be acquired. 

The GLGap model (McKenna and others, 2015) predicted that 63 percent of the stream network should be capable 

of supporting some abundance of Brook Trout. Thirteen 

headwater sites were sampled using backpack electroshocking; two additional high-quality sites judged to be unsuitable 

were not sampled because the bottom substrates were not fit 

for backpack electrofishing. Samples were collected from five 

sites that were predicted to be high quality for Brook Trout 

and, on field inspection, were validated as high quality. Five 

other sites were predicted to be poor quality, but upon inspection, appeared to be of high quality for Brook Trout and also 

were sampled. In addition, three sites were sampled that were 

predicted to be high quality, but were visually of poor quality. 

The mean 1-pass efficiency (Peterson and others, 2004) of 

0.61 for Brook Trout was calculated as the mean of efficiencies 

found at Winnebago Brook (0.69) and at Alder Brook (0.53) 

(table 3). Two of the other common stream species—Blacknose Dace ( Rhinichthys atratulus) and Creek Chub (Semotilus 

Table 2. Estimated surface areas, volumes of water, and exposed reservoir bed above the Hogansburg Dam, 

Franklin County, New York.

[m2, square meters; m3, cubic meters; m, meters]

Reservoir level

Reservoir 

surface area 

(m2

)

Reservoir 

volume 

(m3)

Exposed reservoir bed 

area in m2

 and percent 

of total reservoir bottom 

exposed

Reservoir depth 

in m and percent 

reduction of depth 

Full reservoir 89,054 171,403 0 3.35

 (0 percent) (0 percent)

Remaining water 1 m deep 60,729 54,118 28,325 2.35

(32 percent) (70 percent)

Remaining water 0.5 m deep 44,874 26,513 44,180 2.85

(50 percent) (85 percent)
8 Dam Removal, Connectivity, and Aquatic Resources in the St. Regis River Watershed, New York

atromaculatus)—had efficiencies of 0.47 and 0.58, respectively. 

Total CPUE ranged from 16 to 430 fish/100 m2 (table 4). The 

richness of fish assemblages ranged from 0 to 12, and diversity 

was as high as 1.8. Evenness indicated relatively strong dominance of each assemblage, with all values <0.5, except at site 

ST-E104. In general, these headwater assemblages were dominated by Creek Chub, Brook Trout, and Blacknose Dace. A total 

of 172 Brook Trout were caught from 8 of the sites sampled. 

Brook Trout was the only salmonid present at sampled sites, 

except for site ST-E107, where 23 Brown Trout (Salmo trutta) 

were caught, along with 4 Brook Trout. The average number of 

Brook Trout caught per site was 13.23, and the average length 

was 8.83 centimeters (cm). 

Brook Trout model predictions matched well to observed 

abundances in headwaters of the St. Regis watershed (fig. 1). 

Of the 13 headwater sites sampled, 8 supported Brook Trout. 

Brook Trout were present at only one site where the habitat 

was predicted to be unsuitable (omission error, the fish was 

observed to be present, but was predicted to be absent). High 

abundances (>10) were correctly predicted in three cases and 

moderate abundance (2–10) in one case. In two cases, Brook 

Trout were more abundant than expected (by one abundance 

class). At one site, Brook Trout were present, but less abundant than expected (by one abundance class); in five cases, 

Brook Trout were absent from where the habitat was predicted 

to support moderate or high abundances. The mean water temperature was 11.67 degrees Celsius (°C) for sites where Brook 

Trout were present and averaged 12.97 °C for sites without 

Brook Trout.

The trend in observed Brook Trout abundance appeared 

to be most strongly related to altitude, stream width, and 

water temperature (fig. 4). However, multiple linear regression revealed that none of those habitat variables significantly 

affected Brook Trout abundance, although altitude was nearly 

significant (p = 0.08, R2 = 0.37) (table 5). The pH of these waters also was considered because of known acid rain problems 

in the Adirondacks (mostly granite bedrock, providing very 

little acid buffering capacity), but was weak and insignificant 

(p = 0.52, R2 = 0.039).

Table 3. Sampling efficiency for 1-pass electrofishing for sufficiently calculating 

species abundance near Hogansburg Dam, Franklin County, New York.

Species Site Catch Efficiency (Q) Corrected catch

Brook Trout Winnebago Brook 22 0.69 23

Blacknose Dace Winnebago Brook 17 0.30 26

Brook Trout Alder Brook 35 0.53 39

Creek Chub Alder Brook 136 0.58 147

Blacknose Dace Alder Brook 83 0.64 87

Fathead Minnow Alder Brook 6 0.41 8

Table 4. Fish catch per unit effort (CPUE; standardized abundance in units of fish 

100 square meters), species richness (number of species present), species diversity (ShannonWeaver information index; Shannon and Weaver, 1949), and evenness (index of the distribution 

of total abundance among species present) of fish assemblages in headwater sites near 

Hogansburg Dam, Franklin County, New York. No fish were captured at site ST-E110.

[<, less than]

Brook Trout suitability Site code CPUE Richness Diversity Evenness

High/not suitable ST-E103 24.23 2 0.51 0.16

High/not suitable ST-E104 86.33 12 1.79 0.56

High/not suitable ST-E105 137.20 4 0.83 0.26

High/suitable ST-E100 32.94 6 1.12 0.35

High/suitable ST-E102 76.03 2 0.01 <0.01

High/suitable ST-E108 300.29 10 1.41 0.44

High/suitable ST-E111 430.00 8 1.15 0.36

High/suitable ST-E112 274.58 5 1.09 0.34

Low/suitable ST-E101 378.60 6 1.40 0.44

Low/suitable ST-E106 58.90 1 0 0

Low/suitable ST-E107 88.07 9 1.37 0.43

Low/suitable ST-E109 16.01 3 0.02 0.01
−2.5

−1.5

−0.5

0.5

1.5

2.5

0

10

20

30

40

50

60

70

80

ST-E102 ST-E106 ST-E101 ST-E103 ST-E100 ST-E109 ST-E107 ST-E104 ST-E105 ST-E108 ST-E110 ST-E111 ST-E112

Standard deviation

Brook Trout catch, fish per 100 square meters

+6.88

U.S. Geological Survey site code 

Brook Trout catch

Altitude (meters [m])

Water temperature (degrees Celsius)

Specific conductance (microsiemens per 

 centimeter at 25 degrees Celsius)

Dissolved oxygen (milligrams per liter)

pH

Turbidity

Chlorophyll a

Width sampled (m)

Average depth (m)

Flow (meters per second)

Area of sampled water (square meters)

Volume of sampled water (cubic meters)

EXPLANATION

Figure 4. Habitat characteristics affecting Brook Trout abundance near Hogansburg Dam, Franklin County, New York. (See fig. 2 for site locations.)
10 Dam Removal, Connectivity, and Aquatic Resources in the St. Regis River Watershed, New York
Summary and Conclusions 11

Table 5. Multiple linear regression of Brook Trout abundance as a function of altitude, water temperature, and stream size. 

[t, the statistic of t-test of significance of each model parameter; P, the probability of significance for each parameter of the model; degrees of freedom = 12; 

the F statistic for the overall model = 2.18; the overall model P = 0.16]

Variable Coefficient Standard 

error

t P Lower 

95 percent

Upper 

95 percent

Intercept 6.718 24.957 0.269 0.794 −49.740 63.175

Altitude (feet) 0.019 0.010 1.945 0.084 −0.003 0.041

Water temperature 

(degrees Celsius)

−1.041 1.724 −0.604 0.561 −4.941 2.859

Width sampled (meter) −0.816 2.943 −0.277 0.788 −7.474 5.842

Connectivity Assessment

Removal of the Hogansburg Dam will open 442 km of 

stream habitat within the St. Regis watershed to fish migrating to and from the St. Lawrence River. Migrating fish will 

now be able to reach habitat up to the barriers to connectivity 

indicated in figure 1. Among the headwater sites where Brook 

Trout were collected, all except one are above other natural 

or artificial barriers and will remain isolated after the dam 

is removed. Many other sites that were not sampled, but are 

predicted to have the potential to support Brook Trout, will 

become accessible after the dam is removed. Although there 

are no known major barriers between these sites and the Hogansburg Dam, there are numerous road-crossing culverts and 

many beaver dams that may hinder fish passage.

Thirty-five culverts were inspected in the upper St. Regis 

watershed (fig. 1). Qualitative information about passability, dimensions, and location was collected, and the culverts 

were documented with photos and georeferenced location 

data. Water-quality data also were collected, although pH was 

measured at only 20 sites. Of those 20 sites, 5 had pH <7.0: 

(6.7–5.97); the pH at the 15 other sites ranged from 7.1 to 8.5. 

The majority of culverts were in good working order (33 of 

35) with some level of fish passability. Four sites had evidence 

of beaver activity (nibbled trees), were poorly functioning, and 

(or) had blown-out dams. Six sites had obstructed upstream 

passage via either culvert positioning or nearby man-made 

structures. Seven sites had grates in place, although some had 

fallen over or were out of the water; several could obstruct 

passage, depending on fish body size.

Summary and Conclusions

During this study, the habitat in the immediate vicinity of 

the Hogansburg Dam on the St. Regis River in New York project area was measured and characterized, several components 

of the fish community in the lower St. Regis River were examined, fish assemblages in the headwaters of the watershed were 

examined, the amount of habitat that will become available to 

migratory fish when the dam is removed was estimated, and 

the likely changes to the system (associated with removal of 

this dam) were described. Changes to the system are likely to 

be most significant near the dam removal site—from the head 

of the present reservoir, downstream, possibly to the mouth of 

the river—while headwaters high in the watershed are unlikely 

to be substantially affected. Changes in local aquatic communities and fish movement are expected, as has been reported 

by other work on dam removals (Cooper, 2013; Kornis and 

others, in press).

When the dam is removed, a considerable area of the 

impoundment will be dewatered as the reservoir drains and, 

without active intervention, many freshwater mussels may die 

of exposure due to lower water levels in the former reservoir 

(Stanley and others, 2002; Cooper 2011). The amount of sediment accumulated behind the dam is reported to be relatively 

small (Erie Boulevard Hydropower, written commun., 2012b), 

but most of it is likely to be transported downstream. This may 

result in burial of freshwater mussels and will likely change 

the distribution of sediment below the dam site. That, in turn, 

will alter the amount and distribution of mussel and fish habitat. If the sediment transport is slow, the mussels will likely 

maintain proper depth in the sediment column (Galbraith and 

others, 2015). Eastern Sand Darters may be unaffected or may 

even benefit from the temporary increase in sandy habitat that 

is likely to result. Other aquatic species associated with rocky 

substratum may decline or be displaced initially. Over time, 

much of the sediment will be transported further downstream 

and eventually into the St. Lawrence River. Areas downstream 

of the dam site will experience more dynamic annual flood 

cycles from the upstream watershed. It is unclear whether or 

not the long-term distribution of aquatic habitats will be similar to what presently (2015) exists.

Hundreds of kilometers of stream and river habitat above 

the dam site will become accessible to migratory fish. This 

will allow species including Atlantic Salmon, American Eel, 

Walleye, and Lake Sturgeon to reach spawning areas and 

more easily complete their life cycle. An increased number of 

wetlands also may become available to species like Northern 

Pike, which spawn in flooded wetlands. Whether this expanded access will result in population changes is unknown, but 

genetic exchange between populations of many species above 

and below the dam site will be enhanced (Mahlum and others, 

2014).
12 Dam Removal, Connectivity, and Aquatic Resources in the St. Regis River Watershed, New York

Less desirable species, like Sea Lamprey, also may find 

more extensive spawning ground within the St. Regis watershed after the dam is removed. However, Sea Lamprey already 

have been discovered above the dam (Erie Boulevard Hydropower, written commun., 2012a), and this is not expected to be 

a substantial problem, because they are relatively uncommon 

(Rodger Klindt, New York State—Department of Environmental Conservation, oral commun., 2014) and are not known 

to spawn in St. Lawrence tributaries (Goodyear and others, 

1982). Also, mortality of forage species may increase seasonally due to the migration of piscivores into the areas above the 

dam site (Kornis and others, in press). However, this study 

does not provide data to determine if such changes in mortality would significantly affect the abundances or distributions 

of forage species. Similarly, competition may be enhanced for 

some species above the dam. It is well known that Brook Trout 

populations tend to be displaced from larger streams and rivers 

when Brown Trout are introduced into their habitats. However, most headwater sites sampled in this study, where Brook 

Trout were present, were above other barriers and will not be 

exposed to new migrants; the associated fish assemblages will 

likely remain unaffected by the dam removal. Brown Trout 

already exist in sympatry (live together) with Brook Trout at 

sites within the stream network that will become accessible to 

migratory fish after the dam is removed. Other species within 

the newly accessible stream network also may experience 

increased competition from fish moving into the area from 

below the dam. Again, this study does not provide the data 

needed to evaluate the degree or existence of competition that 

may result. While we examined a number of potential barriers 

or “points of resistance” to passage upstream (poorly performing culverts and beaver dams), no measure is available of how 

much they will impede movement of new migrants upstream.

Headwater populations of Brook Trout appeared to be 

healthy in many habitats, and no particular local habitat variable (including pH) explained their abundance. The relations 

between Brook Trout abundance and habitat variables may be 

non-linear, and multiple interacting affects at a variety of spatial scales are likely to influence them (McKenna and Johnson, 

2011). The match between observed Brook Trout abundances 

and model predictions helped to generally validate the model; 

only a single omission error occurred. This model emphasized 

warm summer air temperatures, but low water temperatures; 

summer precipitation; and percentage of land used for agriculture. The comparison also revealed a number of sites where 

habitat conditions may be degraded below the potential for 

those streams. The five sites without Brook Trout (where they 

were expected to be present, based on the model) could be 

examined to determine if they would be good candidates for 

restoration to improve Brook Trout abundance.

Limitations

This study provides valuable new information about the 

role that the Hogansburg Dam plays in the ecology of the 

St. Regis watershed and what changes may occur when that 

barrier is removed. However, this initial study collected only 

a few samples, particularly near the dam, and only during the 

summer (September). The species observed in the vicinity of 

the dam are relatively common, but more extensive sampling may reveal the presence of less common species. Other 

fish and habitat samples have been collected in association 

with related studies (D.E. Dittman, U.S. Geological Survey, 

written commun., 2009; Erie Boulevard Hydropower, written 

commun., 2012a) and routine collections by the New York 

State-Department of Environmental Conservation (New York 

State-Department of Environmental Conservation, written 

commun., 2002). Use of these data and analyses of broadscale and local habitats together (McKenna and others, 2006; 

McKenna and Johnson, 2011) could reveal more about Brook 

Trout in the headwaters and species communities in the vicinity of the dam. 

More extensive habitat surveys would contribute to better 

predictions of change caused by removal of the dam. For 

example, our estimates from the bathymetric survey are crude. 

The assumptions should be validated with a more extensive 

survey of reservoir depths. More accurate estimates of stored 

sediment volume also would help project the effects of sediment transport on aquatic organisms downstream of the dam 

and would inform the dam removal process. 

It is clear that an extensive portion of the St. Regis River 

watershed stream network will become accessible to migratory fish, including species like American Eel, Atlantic 

Salmon, Walleye, and Sea Lamprey, when the Hogansburg 

Dam is removed. However, the increased amount of spawning, 

nursery, and feeding habitat is not known, nor are the number 

and locations of smaller impediments to upstream migration. Additional sampling for these small barriers and habitat 

conditions within the watershed would help to better understand the ecological changes associated with the dam removal 

(Januchowski-Hartley and others, 2013). A cursory evaluation of road crossing during this study indicates that more 

fish passage-friendly and (or) beaver resistant culverts could 

greatly increase connectivity in the basin (Bigford, 2015). 

Post-removal evaluation is critical to determining the 

value and effects of removing the Hogansburg Dam. Monitoring of fish movements, for game fish and other species, past 

the dam removal site would greatly improve our understanding 

of the importance and extent of fish migrations in the St. Regis 

River system. Extensive monitoring will allow detection of 

migratory fish moving far into the watershed and may indicate 
References Cited 13

habitat use by American Eel, returns of Atlantic Salmon, and 

use of newly accessible esocid (Muskellunge, Esox masquinongy, and Northern Pike) spawning habitats. Evaluation of 

fish assemblages found above and below the dam site at various times after the removal is needed to understand the aquatic 

community changes associated with the barrier removal 

(Kanehl and others, 1997). Repeated sampling in the headwaters will help to determine if any changes could be associated 

with the dam removal. Changes in the distribution of fish 

habitats below the dams should be documented and monitored 

over the time it takes for the sediment that had been stored 

above the dam to move out of the system. Such monitoring 

will reveal significant habitat alterations and allow evaluation 

of ecological changes during the time period in which dam 

removal effects are greatest. A relocation plan for freshwater 

mussels likely exposed by the drawdown could be considered 

and may be required for compliance with the State 401 Water 

Quality Certification. This study and any subsequent investigations can help support management decisions and extend our 

knowledge of the role of artificial barriers and effects of their 

removal. 

Future Research Needs

• More extensive habitat surveys for better predictions of 

changes in aquatic communities and habitats caused by 

dam removal.

• Collect baseline data and generate habitat suitability 

information (HSI) for migratory species, mussels, and 

other aquatic macroinvertebrates that will benefit from 

dam removal including American Eel, Atlantic Salmon, 

Walleye, Sea Lamprey, and Lake Sturgeon; assessment 

of invasive species effects also should be emphasized.

• Identify and prioritize fish passage bottlenecks for 

migratory species above the dam that are associated 

with poor road culverts, beaver activity, etc.

• Use of existing data and landscape models and tools to 

predict changes to Brook Trout in the headwaters and 

species communities in the vicinity of the dam.

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14 Dam Removal, Connectivity, and Aquatic Resources in the St. Regis River Watershed, New York

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Appendix 1 15

Appendix 1. Fish Species Code Definitions

Common name Scientific name

Brown Bullhead Ameiurus nebulosus

Bluegill Lepomis macrochirus

Bluntnose Minnow Pimephales notatus

Brook Trout Salvelinus fontinalis

Brown Trout Salmo trutta

Central Mudminnow Umbra limi

Channel Darter Percina copelandi

Common Shiner Luxilus cornutus

Eastern Sand Darter Ammocrypta pellucida

Fallfish Semotilus corporalis

Fantail Darter Etheostoma flabellare

Fathead Minnow Pimephales promelas

Finescale Dace Phoxinus neogaeus

Golden Shiner Notemigonus crysoleucas

Johnny Darter Etheostoma nigrum

Mimic shiner Notropis volucellus

Muskellunge Esox masquinongy

Northern Pike Esox lucius

Pumpkinseed Lepomis gibbosus

Rock Bass Ambloplites rupestris

Rosyface Shiner Notropis rubellus

Smallmouth Bass Micropterus dolomieu

Spotfin Shiner Cyprinella spiloptera

Silver Redhorse Moxostoma anisurum

Tessellated Darter Etheostoma olmstedi

Walleye Sander vitreus

White Sucker Catostomus commersonii

Yellow Perch Perca flavescens


McKenna, Jr. and others—Dam Removal, Connectivity, and Aquatic Resources in the St. Regis River Watershed, New York—Scientific Investigations Report 2015–5116

ISSN 2328-0328 (online)

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