U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigation Report 2004-5044

Prepared in cooperation with the National Park Service

Effects of Changes in Reservoir Operations on Water Quality 

and Trophic-State Indicators in Voyageurs National Park, 

Northern Minnesota, 2001-03
Effects of Changes in Reservoir Operations 

on Water Quality and Trophic State 

Indicators in Voyageurs National Park, 

Northern Minnesota, 2001-03

By Victoria C. Christensen, Gregory A. Payne, and Larry W. Kallemeyn

Prepared in cooperation with the National Park Service

Scientific Investigation Report 2004-5044

U.S. Department of the Interior

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

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2004

For sale by U.S. Geological Survey, Information Services

Box 25286, Denver Federal Center

Denver, CO 80225

For more information about the USGS and its products:

Telephone: 1-888-ASK-USGS

World Wide Web: http://www.usgs.gov/

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Christensen, V.G, Payne, G.A., and Kallemeyn, L.W., 2004, Effects of changes in reservoir operations on water quality 

and trophic-state indicators in Voyageurs National Park, northern Minnesota, 2001-03: U.S. Geological Survey Scientific Investigation Report 2004-5044, 42 p. 
iii

Contents

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

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

Study area ............................................................................................................................................. 3

Background .......................................................................................................................................... 3

Purpose and scope .............................................................................................................................. 4

Methods ......................................................................................................................................................... 4

Quality assurance and quality control ...................................................................................................... 5

Streamflow .................................................................................................................................................... 8

Reservoir operations .................................................................................................................................... 9

Water-quality results .................................................................................................................................... 9

Physical properties, alkalinity, dissolved solids, and major ions ............................................... 10

Nutrients ............................................................................................................................................. 10

Algal Productivity ............................................................................................................................... 12

Trophic State Indicators ................................................................................................................... 14

Effects on water quality and trophic state ............................................................................................. 15

Historical climate and hydrologic conditions .............................................................................. 15

Comparison with pre-rule curve changes .................................................................................... 15

Comparison of Kabetogama Lake and Black Bay with other lakes .......................................... 18

Summary ...................................................................................................................................................... 19

References .................................................................................................................................................. 20

Appendix ...................................................................................................................................................... 22

Figures

Figure 1. Location of Voyagerus National Park, water-quality sampling sites and gaging 

stations. ......................................................................................................................................... 2

Figure 2. Hydrographs for the three locations where Namakan Reservoir (including 

Namakan Lake and Kabetogama Lake) flows into Rainy Lake (data from Lake 

of the Woods Control Board, 2004). .......................................................................................... 8

Figure 3. International Joint Commission 2000 Rule Curves and 2001-03 lake levels for 

(a) Namakan Reservoir and (b) Rainy Lake. ............................................................................ 9

Figure 4. Monthly data for (a) Secchi-disk transparency, (b) total phosphorus, and 

(c) chlorophyll-a ......................................................................................................................... 12

Figure 5. Boxplots comparing historical baseline concentrations to 2001-03 for (a) total 

ammonia plus organic nitrogen, (b) total phosphorus, (c) dissolved phosphorus, 

(d) chlorophyll-a , and (e) trophic state index. ..................................................................... 17

Tables

Table 1. Sites sampled for baseline water quality, Voyageurs National Park, Minnesota, 

2001-03. .......................................................................................................................................... 4

Table 2. Reporting limits of physical properties measured and water-quality constituents 

sampled in Voyageurs National Park, Minnesota, 2001-03 .................................................. 6
iv

Tables—Continued

Tble 3. Median relative percentage differences for major ions, nutrients, and chlorophyll

 concentrations in replicate samples collected at Rainy and Kabetogama Lakes, 

Voyageurs National Park, Minnesota, 2001-02 ....................................................................... 7

Table 4. Summary of selected physical properties and alkalinity results, Voyageurs National 

Park, Minnesota, 2001-03. ...................................................................................................... 11

Table 5. Summary of selected nutrient analytical results, Voyageurs National Park, 

Minnesota, 2001-03 .................................................................................................................... 13

Table 6. Summary of chlorophyll-a analytical results, Voyageurs National Park, 

Minnesota, 2001-03 .................................................................................................................... 14

Table 7. Comparison of mean August trophic state values based on chlorophyll-a analysis 

for major lakes and bays in Voyageurs National Park, Minnesota .................................. 18

Table 8. Physical properties and alkalinity results by site, Voyageurs National Park, 

Minnesota, 2001-03. .................................................................................................................. 23

Table 9. Dissolved solids and major ion analytical results by site, Voyageurs National 

Park, Minnesota, 2001 ............................................................................................................... 29

Table 10. Nutrient analytical results by site, Voyageurs National Park, Minnesota, 2001-03. ...... 30

Table 11. Chlorophyll analyical results by site, Voyageurs National Park, Minnesota, 2001-03 ... 36

Table 12. Chlorophyll-a and total phosphorus analytical results determined for water

 samples in Voyageurs National Park, Minnesota by the Natural Resource 

Research Institute, 2002-03. ..................................................................................................... 41
v

Conversion Factors

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) 2.471 acre

Flow rate

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

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

 °F=(1.8×°C)+32

Vertical coordinate information is referenced to the insert datum name (and abbreviation) here, 

for instance, “North American Vertical Datum of 1988 (NAVD 88)”

Horizontal coordinate information is referenced to the insert datum name (and abbreviation) 

here, for instance, “North American Datum of 1983 (NAD 83)”

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

*Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.

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 either in milligrams per liter (mg/L) 

or micrograms per liter (μg/L).

NOTE TO USGS USERS: Use of hectare (ha) as an alternative name for square hectometer 

(hm2) is restricted to the measurement of small land or water areas. Use of liter (L) as a special 

name for cubic decimeter (dm3) is restricted to the measurement of liquids and gases. No prefix 

other than milli should be used with liter. Metric ton (t) as a name for megagram (Mg) should be 

restricted to commercial usage, and no prefixes should be used with it.
vi
Abstract

Implementation of an order by the International Joint 

Commission in January 2000 has changed operating procedures for dams that regulate two large reservoirs in Voyageurs 

National Park in northern Minnesota. These new procedures 

were expected to restore a more natural water regime and 

affect water levels, water quality, and trophic status. Results of 

laboratory analyses and field measurements of chemical and 

physical properties from May 2001 through September 2003 

were compared to similar data collected prior to the change 

in operating procedures. Rank sum tests showed significant 

decreases in chlorophyll-a concentrations and trophic state 

indices for Kabetogama Lake (p=0.021) and Black Bay 

(p=0.007). There were no significant decreases in total phosphorus concentration, however, perhaps due to internal cycling 

of phosphorus. No sites had significant trends in seasonal total 

phosphorus concentrations, with the exception of May samples 

from Sand Point Lake, which had a significant decreasing 

trend (tau=-0.056, probability=0.03). May chlorophyll-a 

concentrations for Kabetogama Lake showed a significant 

decreasing trend (tau=-0.42, probability=0.05). Based on 

mean chlorophyll trophic-state indices (2001-03), Sand Point, 

Namakan, and Rainy Lakes would be classified oligotrophic to 

mesotrophic, and Kabetogama Lake and Rainy Lake at Black 

Bay would be classified as mesotrophic. The classification of 

Sand Point, Namakan, and Rainy Lakes remain the same for 

data collected prior to the change in operating procedures. 

In contrast, the trophic classification of Kabetogama Lake 

and Rainy Lake at Black Bay has changed from eutrophic to 

mesotrophic.

Introduction

Voyageurs National Park (hereinafter referred to as the 

Park) contains four large lakes: Sand Point, Namakan, Rainy, 

and Kabetogama (fig. 1). These lakes comprise about 40 percent of the Park. All these lakes existed as natural water bodies 

before dams were built and have been regulated since the early 

1900’s. Rainy Lake is a reservoir unto itself. Namakan Reservoir consists of five connected lakes. Three of the lakes, Sand 

Point, Namakan, and Kabetogama, are in Voyageurs National 

Park. Regulation of both Rainy Lake and Namakan Reservoir 

has altered the magnitude and timing of water-level fluctuations and has removed much of the hydrologic variability the 

Park’s lakes.

Rule curves show bands of permitted maximum and 

minimum water levels that are allowed throughout the year. 

Rule curves give guidance for the operation of a reservoir, and 

daily flow at a dam is set based on the rule curve. The rule 

curves established in 1970 for Rainy and Namakan Reservoirs allowed larger-than-natural fluctuations in lake levels on 

Namakan Reservoir to maintain less-than-natural fluctuations 

on Rainy Lake.

On January 6, 2000, the International Joint Commission (IJC), the international body that sets the rules for the 

operation of dams on waters shared by the United States and 

Canada, issued new rules to restore a more natural water 

regime to the Park’s lakes (Kallemeyn, 2000). The IJC 

encouraged water management agencies to research and monitor the effects of the changes on the ecosystem. Operation 

of the Park’s reservoirs under the new rules will most likely 

change magnitude and direction of water flow between lakes 

in Namakan Reservoir and between Namakan Reservoir and 

Rainy Lake. 

Water flows from Namakan Reservoir into Rainy Lake at 

three locations—through the dams at Squirrel and Kettle Falls 

at the northwest end of Namakan Lake, at Bear Portage on the 

north-central side of Namakan Lake, and at Gold Portage at 

the west end of Kabetogama Lake. The operation of Namakan 

Reservoir under the new rules likely will result in an increase 

in the number of days that water flows through Gold Portage, a natural spillway. When the Namakan Reservoir level 

reaches an elevation of 339.39 m (1113.5 ft) above the North 

Effects of Changes in Reservoir Operations on Water 

Quality and Trophic-State Indicators in Voyageurs 

National Park, Northern Minnesota, 2001-03

By Victoria G. Christensen, Gregory A. Payne, and Larry W. Kallemeyn
2 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

�����

����

����

�����

����

�

��

�

�

��

�

�

��

�

�

��

�

�

��

�

������ ������ ������ ������ ������ ������ ������ ������

������

�������������

�������

���������

����������������

��������������

��

��

���

��� ���

��

������� ����

������

�������

����

����

����

��� ���� �����

��� �����

����� �����

�������

�����

���������

�����

� ��

� �� ����������

�����

���

����� �������

����

����

�������

�������

��������

�������

�������� ���

����

���������

�

�����

�������������

���

���

���

���

���

���

���

� �� ��� �����

� �� ��� ����������

������������

����������

�����������

���������

�������������

��������������

�������������

��������������

�������

���������

������������ ������������

������ ��� ������ ������

���������

������

���������

�

��

��

��

�

��

�� ��

�

��������

��������

�������

�����

������

�������������

���

��������

��������

� � �

� � �

�����

����������

�����������

�����������������������

������������������������

�������������������������

14

��������

��������������������������������

�������

���������

Figure 1. Location of Voyageurs National Park, water-quality sampling sites and gaging stations.
American Vertical Datum of 1988 (NAVD88), water begins to 

spill over into Rainy Lake (International Rainy Lake Board of 

Control and International Lake of the Woods Control Board, 

1984). Streamflow records from the U.S. Geological Survey 

(USGS) gaging station at Gold Portage (1984-98) indicate 

there has been flow through Gold Portage, on average, 253 

days per year. Operating Namakan Reservoir at the midpoint 

(water level) of the new rule curve, as directed by the IJC 

order, would result in flow through Gold Portage about 325 

days per year. If Namakan Reservoir were operated at the 

maximum levels allowed in the order, flow would be expected 

through Gold Portage 365 days per year (Kallemeyn and others, 2003). Increased flow through Gold Portage will result 

in more water from Kabetogama Lake entering Black Bay, 

a shallow, eutrophic bay of Rainy Lake. Increased outflow 

at the west end of Kabetogama Lake also may result in more 

inflow of water from Namakan Lake at the east end of Kabetogama Lake where the two lakes are connected. Evidence of 

Namakan Lake water entering Kabetogama Lake was seen in 

data collected during 1977-84 (Payne, 1991). The effects of 

the rule changes on the Bear Portage outlet of the Namakan 

Reservoir will not be as dramatic as the effects on Gold 

Portage. The outlet sill (elevation) at Bear Portage (approximately 340.39 m or 1,116.8 ft above NAVD88) is 1 m higher 

than the outlet level at Gold Portage. Timing of hydrologic 

events in Namakan Reservoir is expected to change, with peak 

lake-surface elevations, and peak outflow occurring in late 

May to early June, rather than late June to early July. 

The new rules also were proposed to lower phosphorus 

loading into Namakan Reservoir. Changes in water flow 

and phosphorus concentration could dramatically change the 

chemistry and biology of the Park’s lakes, perhaps restoring them to conditions similar to those before the dams were 

built. The chemistry of Namakan and Kabetogama Lakes is 

quite different. Biological production in shallow (less than 

24 m), nutrient-rich Kabetogama Lake is typically 2-3 times 

that in deep, nutrient-poor Namakan Lake. Thus, the change 

in reservoir operation could change the location and quality of 

Namakan Reservoir water delivered to Rainy Lake.

Without a monitoring program in place, it would be 

impossible to determine if the new rule changes are having any 

effect on water quality. The USGS entered into a cooperative 

agreement with the National Park Service (NPS) at Voyageurs 

National Park to study the effects of water-level changes 

on water quality and trophic state. The monitoring program 

established by the agencies will help document these effects 

and evaluate the effectiveness of the IJC’s efforts to alleviate water-quality problems. The specific objectives of this 

study were to gather sufficient water-quality data to document 

changes in primary productivity, nutrient enrichment, and 

major-ion chemistry in the Rainy-Namakan Reservoir system 

due to changes in reservoir operation. Emphasis was placed 

on monitoring nutrients and indicators of biological activity in 

Kabetogama Lake and Black Bay because these water bodies 

were expected to be most affected by the rule-curve changes 

(partially due to the more frequent flow incidence anticipated 

through Gold Portage). 

Study Area

Morphologically, Rainy Lake and Namakan Reservoir 

are typical of lakes located on rocks of the Precambrian shield. 

They have irregular shorelines with numerous rock outcrops 

and islands. Littoral areas with fine-grained sediments are 

primarily restricted to creek or river deltas, or protected 

embayments. In total, Rainy Lake covers 92,000 hectares and 

Namakan Reservoir about 26,000 hectares. The total volume 

of Rainy Lake is about 3 times that of Namakan Reservoir. 

While both Rainy Lake and Namakan Reservoir have maximum depths of about 50 m, there is considerable variation in 

maximum and mean depth between individual lake basins. 

The maximum depth of Kabetogama Lake is about 24 m and 

the mean depth is about 9 m. While thermoclines are typically present throughout summer in the deeper basins, thermal 

stratification occurs infrequently in Kabetogama Lake. When 

Kabetogama Lake is thermally stratified, dissolved oxygen 

concentrations below the thermocline are usually less than the 

accepted standards for aquatic life. The lakes are typically ice 

covered for about 5 or 6 months per year, with ice-up occurring in mid- to late November and ice-out occurring about 

May 1. 

Background

Sand Point, Namakan, and Rainy Lakes, which receive 

most of their inflow from drainage areas with large areas of 

exposed bedrock and thin noncalcareous glacial sediments, 

have been characterized as oligotrophic to mesotrophic, 

and have low dissolved solids and alkalinity. In contrast, 

Kabetogama Lake, which receives much of its inflow from 

an area overlain by calcareous glacial sediment, has been 

characterized as eutrophic, and has greater dissolved solids 

and alkalinity. A baseline water-quality study during 1977-84 

(Payne, 1991) reported samples collected in a stream near the 

west end of the Park had dissolved-solid concentrations about 

five times and total alkalinity concentrations about eight times 

concentrations measured in the Namakan River (fig. 1). The 

baseline study was conducted to determine major water types 

and characteristics of the large lakes and bays in Voyageurs 

National Park. A subsequent study during 1999 (Payne, 2000) 

was conducted and results were compared to the data collected 

during 1977-84. The results showed that specific conductance 

and alkalinity values from 1999 were similar to those from 

the 1977-84 study. Nitrite plus nitrate nitrogen concentrations 

generally were lower throughout the Park and total phosphorus 

concentrations were lower in Kabetogama Lake and Rainy 

Lake at Black Bay (hereinafter referred to as Black Bay) relative to the baseline study. Trophic state indices (TSI), based on 

chlorophyll-a concentrations (Carlson, 1977), indicated lower 

algal biomass throughout the Park. The largest decreases in 

Introduction 3
4 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

algal biomass in 1999, relative to the baseline study, were in 

Kabetogama Lake, Black Bay, and Sullivan Bay.

Hargis (1981) measured chlorophyll-a concentrations in 

the summer of 1979. These chlorophyll-a values were used 

to calculate trophic state indices for stations in each of the 

four large lakes in the Park. Kepner and Stottlemyer (1988) 

converted the Hargis data to lakewide means and compared 

it to their own data collected in 1985 and 1986. There were 

no obvious trends in TSI between 1979 and 1986. TSI values 

reported by Kepner and Stottlemyer ranged from 40-54 in 

Sand Point, 34-46 in Namakan, 36-50 in Rainy, and 44-65 in 

Kabetogama.

Kepner and Stottlemyer (1988) reported values for specific conductance, chlorophyll-a concentrations, and carbon 

assimilation rates from Kabetogama Lake that typically were 

2 to 3 times greater than those from the three less productive 

lakes. Analysis with a total-phosphorus mass-balance model 

indicated the peak total-phosphorus concentrations in Kabetogama Lake, which occur during spring, would be reduced 

from about 0.034 to 0.030 mg/L if the previous rule curves 

(International Joint Commission Order Prescribing Method 

of Regulating the Levels of Boundary Waters, Supplementary 

Order dated July 29, 1970) were replaced by one approximating natural conditions. The authors attributed this to (1) a 

reduction in bottom areas exposed by drawdown and accompanying sediment-water interactions, (2) reduced nutrient 

inputs resulting from die-off of littoral vegetation, and (3) 

reduced nutrient concentrations due to changing (rather than 

constant) volume. The authors, stressing that the model was 

uncalibrated, concluded a return to natural fluctuations could 

reduce phytoplankton biomass and the accompanying primary 

production. These changes, in turn, could have ramifications 

throughout the food web.

Purpose and Scope

The purpose of this report is to describe effects of 

changes in reservoir operations on water quality and trophic 

state in Voyageurs National Park. Data collected in 2001-03 

are described and compared to data collected in 1977-83, 

1985, and 1986. This report will attempt to answer the following questions: (1) Are changes in primary productivity 

and nutrient enrichment, relative to baseline data, taking 

place in Kabetogama Lake and Black Bay, post January 2000 

rule-curve change? (2) Are changes in primary productivity 

and nutrient enrichment in Kabetogama Lake and Black Bay 

greater than changes at reference sites in Sand Point Lake, 

Namakan Lake, and Rainy Lake?

Answers to these questions are intended to establish a 

baseline for comparison with future studies of reservoir operation. Results also may contribute toward improved understanding of how water levels may affect water quality. 

Methods

Nine sampling sites were selected for the 2001-03 study 

described in this report. Six sampling sites correspond to those 

used for collection of baseline water-quality data as described 

and numbered in Payne (1991). These are Site 7 in Sand Point 

Lake, Site 14 in Namakan Lake, Site 5 in Rainy Lake, Site 11 

in Kabetogama Lake, and Sites 1 and 16 in Black Bay. Rainy 

Lake at Black Bay near International Falls (Site 16) was not 

sampled after June 9, 2003 due to low water, which made boat 

access difficult. Two additional sites were established in Kabetogama Lake (43 and 45) and one additional site was established in Black Bay (44) (fig. 1). A list of the sites sampled 

during the current study and their corresponding USGS station 

and site numbers are listed in table 1. 

Water-quality monitoring was most intensive in Kabetogama Lake and Black Bay. Water samples were collected at 

2-week intervals from May through October at three sites in 

Kabetogama Lake and at three sites in Black Bay (Sites 11, 

43, and 45; and 1, 16, and 44; respectively, fig. 1). Samples 

were analyzed to determine concentrations of chlorophyll-a 

and total phosphorus. Secchi-disk transparency and vertical profiles of specific conductance, pH, temperature, and 

dissolved oxygen were measured at each site during each 

sampling. Barometric pressure was measured for use in the 

calibration of dissolved oxygen meters.

USGS station number Site number (figure1)

482226092283301 Sand Point Lake below Harrison Narrows near Crane Lake 7

482616092372201 Namakan Lake near Ray 14

483622092560701 Rainy Lake at Brule Narrows near International Falls 5

482607092511701 Kabetogama Lake at Mouth of Meadwood Bay near Ray 11

483012093035001 Kabetogama Lake at Cemetary Island near Ray 43

482731092574701 Kabetogama Lake near Grave Island near Ray 45

483511093092801 Rainy Lake at Black Bay Narrows near International Falls 1

483304093062701 Rainy Lake at Black Bay near International Falls 16

483341093111501 Rainy Lake at Black Bay (West) near International Falls 44

Table 1. Sites sampled for baseline water quality, Voyageurs National Park, Minnesota, 2001-03.
During May and August, the Kabetogama and Black Bay 

sites were sampled for determination of additional constituents, including alkalinity, dissolved solids, and dissolved 

magnesium, calcium, sodium, potassium, manganese, chloride, sulfate, nitrite nitrogen, and nitrite plus nitrate-nitrogen, 

dissolved ammonia, dissolved and total ammonia plus organic 

nitrogen, dissolved phosphorus, dissolved ortho-phosphorus, 

and chlorophyll-b. Dissolved nitrate nitrogen was calculated 

for these samples by subtracting dissolved nitrite from dissolved nitrite plus nitrate results. Three additional sites were 

sampled during May and August at locations in Sand Point, 

Namakan, and Rainy Lake (Sites 7, 14, and 5, respectively, fig. 

1). These additional sites were used for comparative purposes. 

Sampling for major ions was intended to provide information on the extent of water exchange between Namakan Lake, 

Kabetogama Lake, and Black Bay. Sampling for major ions 

was discontinued after 2001 and therefore, the analysis of 

water exchange is limited. 

A list of physical properties measured, water-quality constituents analyzed, reporting units and method reporting limits 

are listed in table 2. Reporting limits indicated by less than (<) 

values in analytical results, can be different from the method 

reporting limits because of sample matrix effects and other 

sources of variability. Physical properties measured at the field 

site included air pressure, specific conductance, pH, water 

temperature, transparency, and dissolved oxygen. Specific 

conductance, water temperature, pH, and dissolved-oxygen 

concentration were measured using portable field instruments. 

Although observations of field values were recorded throughout the water column, only those obtained at the Secchi depth 

are reported herein.

Depth of water transparency was measured using a standard black and white Secchi disk, a metal disk painted with 

alternate quadrants of black and white. The disk is lowered 

from the water surface to determine light penetration through 

the water. Because of its historical use at the Park, the Secchidisk transparency is an important reading to show temporal 

change in water clarity. Although more accurate methods of 

measuring water clarity are available, Secchi-disk measurements are popular because they are simple and inexpensive. 

Secchi-disk readings do, however, have their limitations. They 

depend on the eyesight of the viewer, the time of day, the 

color of the water, and the condition of the disk. These limitations should be kept in mind when comparing readings either 

through time or from site to site. 

Samples of water were collected from top, center, and 

bottom positions in the water column. The top subsample was 

collected at a depth of less than 1 m, the center subsample was 

collected at the depth of the Secchi disk reading, and the bottom subsample was collected at twice the depth of the Secchi 

disk reading. Samples were collected using a Van-Dorn type 

sampler. Subsamples were composited (equal-volume) into 

bottles and placed in coolers with ice immediately after collection. 

Water samples were processed in a field laboratory on 

site or in a laboratory vehicle where they were filtered and preserved as required. Alkalinity was determined by incremental 

titration at the field laboratory. Measured volumes of composite whole water for determination of chlorophyll-a and b were 

filtered in the field laboratory and the filter containing the 

algal material was packaged and frozen immediately. Samples 

were shipped from the field laboratory to the USGS National 

Water-Quality Laboratory (NWQL) in Denver, Colorado using 

commercial next-day delivery. The NWQL reports estimated 

(E) values for several reasons, including when constituents 

were detected below the method reporting level, the concentrations were outside the calibration range, or there was a deviation in the standard operating procedure. In tables of NWQL 

data within this report, estimated values were used in the 

computation of means and medians. Mean and median values 

were not computed for data sets with more than one censored 

value (less than). For those data sets with only one censored 

value, one-half that value was used in the calculation of mean 

and median concentrations. 

The Natural Resources Research Institute (NRRI), in 

Duluth, Minnesota, analyzed additional biweekly water 

samples (for phosphorus and chlorophyll, using EPA 365.3 

and Standard Method 10200, respectively (John Ameel, Natural Resources Research Institute, written commun., February 

16, 2004)). Analytical results from the NWQL and NRRI are 

reported in separate tables (tables 10-12, appendix). Statistical tests were performed on NWQL data only, so as not to 

misinterpret differences among the lakes and bays from differences which may result from analytical variability between the 

NWQL and NRRI.

Separate data sets were analyzed by NRRI and Braun 

Intertec Corporation, Minneapolis, Minnesota to assess spatial 

variability. These data are discussed in the Quality Assurance 

and Quality Control section of this report. Braun Intertec Corporation analyzed phosphorus using USEPA method 365.4 and 

chlorophyll-a using Standard Method 10200 (Steven Albrecht, 

Braun Intertec, written commun., August 7, 2003).

Streamflow and lake-elevation data were gathered from 

gaging stations currently in operation at Gold Portage Outlet at Kabetogama Lake (USGS station number 05129290), 

Namakan River at Outlet of Lac La Croix (USGS station 

number 05128000), Rainy Lake near Fort Francis (USGS station number 05129400), and Vermillion River near Crane Lake 

(USGS station number 05129115). Additional streamflow data 

was gathered from Squirrel and Kettle Falls and Bear Portage.

Quality Assurance and Quality Control

A primary data quality objective was to ensure that 

samples were representative of the water bodies under investigation. Quality assurance was assessed with specific procedures, such as instrument calibration, to ensure data reliability. 

To understand the error associated with the sample data, 11 of 

the 44 full-suite samples collected and analyzed by the NWQL 

were quality control samples (field blanks or replicates). 

Methods 5
6 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Spatial variability also was assessed through the collection of 

samples from randomly selected sites in Kabetogama Lake.

Instrument calibration for portable field instruments was 

undertaken at the start of each day and was verified at the end 

of each day. More frequent calibration was initiated if end-ofday verifications indicated that instruments were not holding 

calibration. Observations of physical properties in the water 

column (specific conductance, temperature, pH, and dissolved 

oxygen) were recorded at 1 m intervals normally, but submeter 

intervals were used when specific conductance changed more 

than 5 percent per meter, temperature changed more than 1 

degree Celsius per meter, or pH changed more than 0.5 unit 

per meter. Submeter recording intervals also were used to 

more precisely delineate any part of the water column where 

dissolved-oxygen concentrations were less than 5 mg/L. 

Effectiveness of equipment cleaning and sample processing was assessed by laboratory analysis of field blanks. To 

quality assure equipment and procedures used in the field, 

Physical property or constituent

Field 

instrument

Reporting limit

National WaterQuality Laboratory

Braun Intertec 

Corporation

Natural 

Resources Research 

Institute

Air pressure 1 mm -- -- --

Specific conductance, field 1 μs/cm -- -- --

Specific conductance, laboratory -- 1 μs/cm -- --

Field pH 0.1 unit -- -- --

Laboratory pH - 0.1 unit -- --

Water temperature 0.1  ̊C -- -- --

Transparency, Secchi disk 0.1 m -- -- --

Dissolved oxygen 0.1 mg/L -- -- --

Dissolved calcium -- 0.025 mg/L -- --

Dissolved magnesium -- 0.008 mg/L -- --

Dissolved sodium -- 0.06 mg/L -- --

Dissolved potassium -- 0.09 mg/L -- --

Bicarbonate alkalinity as HCO3 -- 1 mg/L -- --

Carbonate alkalinity, as CO3 -- 1 mg/L -- --

Total alkalinity as CaCo3 -- 1 mg/L -- --

Dissolved sulfate -- 0.11 mg/L -- --

Dissolved chloride -- 0.08 mg/L -- --

Dissolved nitrite nitrogen -- 0.001 mg/L -- --

Dissolved nitrite plus nitrate nitrogen -- 0.005 mg/L -- --

Dissolved ammonia nitrogen -- 0.002 mg/L -- --

Dissolved ammonia plus organic nitrogen -- 0.1 mg/L -- --

Total ammonia plus organic nitrogen -- 0.1 mg/L -- --

Total phosphorus -- 0.004 mg/L 0.01 mg/L 0.007 mg/L

Dissolved phosphorus -- 0.004 mg/L -- --

Dissolved orthophosphorus -- 0.001 mg/L -- --

Dissolved manganese -- 3.0 μg/L -- --

Chlorophyll-a -- 0.1 μg/L 0.5 μg/L 0.01 μg/L

Chlorophyll-b -- 0.1 μg/L -- --

Table 2. Reporting limits of physical properties measured and water-quality constituents sampled in Voyageurs National Park, Minnesota, 2001-03

[°C, degrees Celsius; m, meters; μS/cm, microsiemens per centimeter at 25 °C; mg/L, milligrams per liter; μg/L, micrograms per liter; --, not analyzed]
laboratory blank water was processed through collection 

bottles and filtering devices using the same methods as for 

native water samples. Results of analysis performed on these 

blanks showed little evidence of sample contamination. Concentrations for all blank samples collected in 2001 and 2002 

were less than the method reporting limit (MRL) for each 

constituent (table 2). A blank water sample processed on May 

28, 2003 had concentrations less than the MRL for all constituents with the exception of ammonia, which was detected at a 

concentration of 0.027 mg/L (MRL 0.002 mg/L).

For this study, within-site variability associated with 

sample collection and analysis was determined through the 

collection of replicate samples from Rainy Lake at Black Bay 

Narrows near International Falls (Site 1), Rainy Lake at Brule 

Narrows near International Falls (Site 5), and Kabetogama 

Lake near Grave Island near Ray (Site 45). Samples were 

collected following procedures used during the baseline study 

(Payne, 1991) for comparability with historical data. Results 

of analysis of the replicate samples are shown in table 3. A 

typical quality-control objective for precision of replicate 

samples is a maximum relative percentage difference of 20 

percent (Taylor, 1987). The median relative percentage difference was less than 20 for all constituents; however, one paired 

sample collected on May 15, 2001 at Rainy Lake at Brule 

Narrows showed a relative percentage difference of 40 percent 

for ammonia, 22 percent for chlorophyll-a, and 29 percent for 

chlorophyll-b. The ammonia and chlorophyll-b concentrations 

were close to their method detection limit, which may account 

for the increased variability. These percentage differences 

need to be taken into account when evaluating the variability 

between samples from the same site. 

To assess intrabasin spatial variability of limnological 

characteristics in Kabetogama Lake, an additional nine sites 

were sampled along with Sites 11, 43, and 45 (fig. 1) on June 

20-21, 2003, and July 18, 2003. The nine sites were randomly 

selected using a geographic information system from the portion of the lake where water depths equaled or exceeded 5 m. 

Voyageurs National Park staff and volunteers from the North 

Star Chapter of the Academy of Hazardous Materials Managers conducted sampling at these sites. Samples were collected 

using the same field procedures as previously described for 

Sites 11, 43, and 45 (Payne, 1991). Total phosphorus and 

chlorophyll-a analyses for the June samples were completed 

at the NRRI in Duluth, Minnesota, and for the July samples 

at Braun Intertec Corporation, Minneapolis, Minnesota. No 

comparisons were made between the June and July samples 

because different laboratories were used and no replicates 

between laboratories were analyzed. The data tables for the 

Constituent

Median relative percentage 

difference

Pairs of replicate 

samples

Dissolved solids (mg/L) 0.0 1

Dissolved calcium (mg/L) 3.1 1

Dissolved magnesium (mg/L) 2.3 1

Dissolved potassium (mg/L) 4.3 1

Dissolved sodium (mg/L) 7.1 1

Dissolved chloride (mg/L) 10.6 1

Dissolved sulfate (mg/L) 5.7 1

Dissolved manganese (μg/L) 1.3 1

Dissolved nitrite nitrogen (mg/L) 0.0 2

Dissolved nitrite plus nitrate nitrogen (mg/L) 9.1 2

Dissolved ammonia nitrogen (mg/L) 20.0 2

Dissolved ammonia plus organic nitrogen (mg/L) 6.3 2

Total ammonia plus organic nitrogen (mg/L) 7.4 2

Total phosphorus (mg/L) 8.7 3

Dissolved phosphorus (mg/L) 4.4 2

Dissolved orthophosphorus (mg/L) 9.1 2

Chlorophyll-a (μg/L) 15.7 2

Chlorophyll-b (μg/L) 14.3 2

Table 3. Median relative percentage differences for major ions, nutrients, and chlorophyll concentrations in replicate samples collected 

at Rainy and Kabetogama Lakes, Voyageurs National Park, Minnesota, 2001-02

.[ mg/L, milligrams per liter; μg/L, micrograms per liter]

Quality assurance and quality control 7
8 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

spatial analysis are not contained in this report, and are on 

file at the Voyageurs National Park Office, International Falls, 

Minnesota. A summary of the spatial analysis follows. 

Values for total phosphorus and chlorophyll-a from the 

Sites 11, 43, and 45 were generally within the range of values 

from the additional nine sites. In June, total phosphorus concentrations at Sites 11, 43, and 45 (0.014, 0.012, 0.010 mg/L) 

were within the range of values from the nine additional sites 

(0.06 – 0.016 mg/L, mean 0.011). The chlorophyll-a concentration at Site 43 in June was 2.84 μg/L, which was 0.34 

μg/L greater than the maximum concentration observed at 

any of the nine sites. Chlorophyll-a concentrations at Sites 45 

(1.84 μg/L) and 11 (1.67 μg/L) were within the range of 0.67 

to 2.50 μg/L measured at the other nine sites.

Except for total phosphorus at Site 11 (0.014 mg/L), 

concentrations in July at Sites 11, 43, and 45 were within the 

range of values from the nine additional sites. Total phosphorus concentrations at Sites 43 and 45 were 0.018 and 0.017 

mg/L, respectively, while the range for the nine sites was 

0.016–0.026 mg/L. The range for chlorophyll-a was 5.4–21.0 

mg/L (mean 9.8 mg/L), and the concentrations at Sites 11, 43, 

and 45 were 5.7, 6.9, and 9.1 mg/L, respectively. 

Streamflow 

Water generally flows through Voyageurs National 

Park from the southeast to the northwest along the United 

States/Canada border. On average 109 m3

/sec flow from the 

Namakan River into the Park annually (Kallemeyn and others, 

2003). Combined with an average of 9 m3

/sec from the Vermillion River, this accounts for 80 percent of the inflow to the 

Namakan Reservoir. 

Water flows from Namakan Reservoir into Rainy Lake at 

four locations—Squirrel and Kettle Falls, Gold Portage, and 

Bear Portage (fig. 1). Most of this flow discharges through 

the adjacent regulated dams at Squirrel and Kettle Falls. The 

quantity of water that moved from Namakan Reservoir to 

Rainy Lake from 2001 to October 2003 is represented by the 

hydrographs for Squirrel and Kettle Falls, Gold Portage, and 

Bear Portage (fig. 2).

��������������������������������

���

���

���

���

���

���

�

������������

������������

������������

������������

������������

������������

������������

������������

������������

������������

������������

������������

���

������������

������������

������������

������������

Figure 2. Hydrographs for the three locations where Namakan Reservoir (including Namakan Lake and Kabetogama Lake) flows into 

Rainy Lake (data from Lake of the Woods Control Board, 2004).
Reservoir Operations

The new rule curves were implemented on January 6, 

2000 for regulating water levels on Rainy Lake and Namakan 

Reservoir. The requisite maximum and minimum water levels 

as defined by the IJC for Namakan Reservoir are shown in figure 3a. The actual water levels also are shown. The rule curve 

levels and actual levels for Rainy Lake are shown in figure 3b. 

During 2001 and 2002, the maximum rule curve water 

levels were exceeded during late spring and early summer. 

According to the IJC, at the end of March 2001, there was 

near-normal water content in the snowpack, normal to greater 

than normal soil moisture and well below normal baseflow in 

the basin’s rivers and streams (International Rainy Lake Board 

of Control and International Rainy River Water Pollution 

Board, 2002). Two substantial periods of rainfall in the spring 

(mid-April to mid-June) and summer (late July) caused the 

high water levels and flows in spring and summer 2001. High 

water level conditions existed not only in the Rainy-Namakan 

Basin, but extended downstream to the Lake of the Woods. On 

Rainy and Namakan Lakes the 2001 levels were the highest 

since 1968 (International Rainy Lake Board of Control and 

International Rainy River Water Pollution Board, 2002). 

Rainy Lake also experienced very high water levels in 

2002 due to heavy rainfall on June 9 and 10 and June 22-23. 

On Rainy Lake, the 2002 peak level was the highest since 

1950 (International Rainy Lake Board of Control and International Rainy River Water Pollution Board, 2002). A decrease 

in Namakan Reservoir outflow along with localized heavy 

rainfall on July 4-5, 2002 over the Namakan Lake and its 

tributaries contributed to high levels on Namakan Reservoir. 

Very dry conditions from November 1, 2002 through 

March 31, 2003 resulted in low water conditions on Rainy 

Lake and Namakan Reservoir. Measured precipitation during 

this period was the least since 1901 (International Rainy Lake 

Board of Control, news release May 30, 2003). Dry conditions 

continued through the summer of 2003, with Namakan Reservoir levels remaining near the lower rule curve and Rainy Lake 

levels about 1 m below the lower rule curve (fig. 3).

Changes in timing of peak lake-surface elevations in 

Namakan Reservoir did not occur as expected. Although the 

peak elevation occurred earlier as expected in 2001, the 2002 

peak elevation occurred around July 1 as it had before the rule 

curve change. The peak elevations may have been affected by 

extreme rainfall experienced throughout Northwest Minnesota 

(Wiche and others, 2002). In 2003, a year of drought conditions, peak lake-surface elevation occurred much later (fig. 3).

On the basis of streamflow records from the USGS gaging station at Gold Portage (1984-2000), flow occurred on 

average for 253 days per year under the IJC 1970 order. Under 

the IJC’s 2000 order flow occurred an average for 312 days per 

year (365 in 2001, 344 in 2002, and 227 in 2003). Namakan 

Reservoir was operated near the maximum of the IJC 2000 

order during most of 2001 and exceeded the maximum during high flows in the spring and summer. During 2002, the 

reservoir operated closer to the midpoint of the IJC rule curve, 

but still exceeded the maximum during summer high flows. 

However, after two years of high flows (2001 and 2002), the 

area had drought conditions in 2003 and the reservoir operated 

substantially below the minimum rule curve during the second 

half of 2003. A beaver dam constructed in Gold Portage in 

early summer further restricted outflow. As a result of drought 

conditions and the beaver dam the incidence of flow through 

Gold Portage was less than predicted. 

Water-Quality Results

Results of analyses of physical properties, alkalinity, dissolved solids, major ions, nutrients and chlorophyll 

were evaluated to determine the major characteristics, water 

types, and algal productivity of the lakes and bays (tables 

8-12, appendix). The baseline study (Payne, 1991) divided 

the waters of the Park into three groups on the basis of the 

characteristics of specific conductance, transparency, alkalin-

������������

������������

������������

������������

������������

������������������������

������������

������������

������������

������������

������������

���

��������������������

�����

�����

�����

�����

�����

�����

�����

�����������

�����

������������������

������

�����������

�����

������������

������������

������������

������������

������������

������������������������

������������

������������

������������

������������

������������

��������������������

�����

�����

�����

�����

�����

�����

�����

�����������

�����

�����������

������

�����������

�����

���

Figure 3. International Joint Commission 2000 Rule Curves and 2001-03 lake levels for (a) Namakan Reservoir and (b) Rainy Lake.

Reservoir operations 9
10 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

ity, nutrient concentrations, and algal productivity. The groups 

were (1) Sand Point (Site 7), Namakan (Site 14), and Rainy 

Lakes (Site 5); (2) Kabetogama Lake (Sites 11, 43, and 45) 

and Black Bay (Sites 1, 16, and 44); and (3) Sullivan Bay. 

In each of these characteristics, the water bodies in groups 1 

and 3 were at opposite extremes, whereas characteristics of 

Kabetogama Lake and Black Bay were approximately midway 

between the extremes. Sullivan Bay was not sampled during 

the current study (2001-03); however, the samples collected 

during 2001 through 2003 indicate that Sand Point, Namakan, 

and Rainy Lakes continue to show similar characteristics, 

whereas Kabetogama Lake and Black Bay have substantially 

different water-quality characteristics than the other lakes. 

During the 2001-03 study, samples also were used to 

determine water quality in the Park with respect to established water-quality criteria. Sand Point, Namakan, Rainy, 

and Kabetogama Lakes are classified by the State of Minnesota for domestic consumption, aquatic life and recreation, 

and industrial consumption (Minnesota Rules, Chapter 

7050.0470). The quality of these waters must meet the primary 

(maximum contaminant levels) and secondary drinking water 

standards issued by the U.S. Environmental Protection Agency 

(USEPA). Results were compared to criteria established by 

the USEPA for drinking water, recreation, and protection of 

aquatic life (USEPA, 1986). Most of the constituents and 

properties listed in table 2 that have USEPA criteria were 

within recommended limits. An exception was dissolved 

oxygen, which occurred below the USEPA standard of 5 

mg/L in Kabetogama Lake and Black Bay at least once at 

four sampling sites during the study. In addition, pH values at 

times exceeded the USEPA guideline of 8.5 in Kabetogama 

Lake and Black Bay. Dissolved oxygen concentrations below 

5 mg/ L can seriously impair the aquatic ecosystem. Levels 

of pH typically rise above 8.5 under intense photosynthesis 

and indicate high alkalinity, which may affect the taste of the 

water.

For all constituent concentrations presented in this section, the percentage differences (table 3) in the quality control 

samples need to be considered. This is particularly important 

for dissolved chloride, dissolved ammonia nitrogen, and chlorophyll-a and –b, all of which had median relative percentage 

differences for replicate samples greater than 10. 

Physical properties, alkalinity, dissolved solids, 

and major ions

A summary of selected physical properties and alkalinity results for the nine sites are shown in table 4. Analyses 

for dissolved solids and major ions were discontinued at the 

end of the first sampling season, and are of limited value for 

showing trends or providing information on the extent of 

water exchange between the lakes. Data presented in figure 4 

for Black Bay and Kabetogama Lake represent the means for 

samples collected at the three sites in Black Bay (Sites 1, 16, 

and 44) and the three sites in Kabetogema Lake (Sites 11, 43, 

and 45).

Secchi-disk transparency varied seasonally as well as 

annually at some sites during 2001 through 2003 (fig. 4). 

Secchi-disk transparencies for Black Bay generally were 

shallower than transparencies for the other lakes and peaked 

(deepest transparencies) in late June. During 2003, the Sand 

Point, Namakan, and Rainy Lakes not only had deeper transparencies, but also showed a different pattern with at least 

one peak occurring in August. Kabetogama Lake had deeper 

transparencies than Black Bay for all 3 years. Secchi-disk 

transparencies that are shallower during the summer season 

may be due to increased amount of algae (possibly caused by 

decreased zooplankton that graze on the algae), recirculation 

of bottom sediment due to motorboat activity or wind action, 

increased runoff, or plant decomposition. Blue green algae 

blooms contribute to shallower Secchi-disk transparencies 

from late July through August in Kabetogama Lake (Kallemeyn and others, 2003).

Specific conductance and alkalinity values generally were 

greater in Black Bay and Kabetogama Lake when compared 

to the other three lakes. Dissolved solids also were greater in 

Black Bay and Kabetogama Lake, as was dissolved calcium 

and magnesium (table 9, appendix). Dissolved concentrations 

of sodium, potassium, sulfate, and chloride did not follow this 

pattern. Potassium was smallest in Namakan Lake and Rainey 

Lake (Site 5). The greatest concentrations of sodium, sulfate, 

and chloride were measured in samples from Sand Point Lake. 

The relative proportions of the major cations (calcium, magnesium, sodium, and potassium) for each lake are similar to the 

proportions reported in the baseline study (Payne, 1991).

Nutrients 

Nitrogen and phosphorus are essential for the growth and 

reproduction of plants. Rooted aquatic plants and algae require 

dissolved forms of nitrogen and phosphorus as nutrients. 

Compounds of nitrogen, such as nitrate, nitrite, and ammonia, 

are the basic building blocks for protein synthesis, whereas 

phosphorus serves as an energy source in cellular chemical 

reactions. Large inputs of nitrogen compounds and phosphorus 

into the aquatic environment can cause excessive algal growth. 

This may reduce the aesthetic and recreational value of water, 

and stress aquatic organisms, resulting from depleted dissolved oxygen concentrations when algal blooms die. Therefore, it is desirable to prevent or mitigate the introduction of 

excessive nutrient concentrations into surface water where 

sensitive aquatic organisms may be present. 

Total phosphorus concentrations are shown in figure 

4b. Kabetogama Lake and Black Bay generally had greater 

concentrations of total phosphorus from 2002-03 than Sand 

Point, Namakan, and Rainy Lakes. Greater mean total phosphorus concentrations in summer indicate that there is an input 

of phosphorus during the summer season from either external 

(inflow or precipitation) or internal (lake sediments) sources 
Water 

Temperature 

(°C)

Secchi disk 

transparency (m)

Specific 

conductance, field 

(μS/cm) Field pH

Dissolved oxygen 

(mg/L)

Total 

alkalinity as 

CaCO3 (mg/L)

Bicarbonate 

alkalinity as 

HCO3 (mg/L)

Sand Point Lake below Harrison Narrows near Crane Lake, Site 7

minimum 2.2 1.3 55 7.0 6.9 16 20

maximum 25.2 3.3 82 7.7 11.8 21 25

mean 15.5 2.4 69 7.4 9.5 19 23

median 17.0 2.3 69 7.4 9.7 20 24

Namakan Lake near Ray, Site 14 

minimum 5.2 2.1 37 6.7 7.4 14 17

maximum 25.3 4.1 55 7.9 12.7 16 20

mean 16.7 3.0 48 7.3 9.7 15 19

median 18.2 3.0 48 7.2 9.2 16 20

Rainy Lake at Brule Narrows near International Falls, Site 5

minimum 6.2 2.0 42 6.5 7.2 14 17

maximum 23.7 3.0 64 8.2 13.1 16 20

mean 16.3 2.5 49 7.2 9.6 15 19

median 17.7 2.3 48 7.3 9.0 15 19

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11

minimum 8.0 1.2 57 7.0 4.7 22 27

maximum 26.8 3.7 118 9.2 12.2 56 68

mean 18.4 2.1 90 7.9 9.0 39 48

median 19.5 2.1 96 7.7 8.7 39 48

Kabetogama Lake at Cemetary Island near Ray, Site 43 

minimum 7.6 1.2 64 6.6 5.1 34 41

maximum 25.2 4.0 106 9.1 13.3 58 71

mean 18.0 2.2 94 7.8 8.9 42 51

median 19.6 2.2 96 7.7 8.9 40 49

Kabetogama Lake near Grave Island near Ray, Site 45 

minimum 6.8 1.1 65 7.3 4.9 31 38

maximum 25.6 3.3 109 9.2 12.8 56 68

mean 18.1 2.2 94 7.9 9.0 42 51

median 19.5 2.2 96 7.8 9.0 41 50

Rainy Lake at Black Bay Narrows near International Falls, Site 1

minimum 5.5 0.3 55 7.1 6.0 20 24

maximum 29.5 1.5 108 8.5 13.3 54 66

mean 17.9 0.9 86 7.7 8.9 35 43

median 18.0 0.9 92 7.7 8.5 36 44

Rainy Lake at Black Bay near International Falls, Site 16 

minimum 6.1 0.3 42 7.3 3.9 35 43

maximum 26.9 1.8 104 8.8 13.5 42 51

mean 17.5 0.9 90 7.8 8.7 38 47

median 18.0 0.9 93 7.7 8.8 38 47

Rainy Lake at Black Bay (West) near International Falls, Site 44

minimum 5.5 0.1 61 6.4 4.7 33 40

maximum 27.3 2.2 157 9.1 13.2 59 72

mean 18.2 0.6 102 7.6 8.3 43 52

median 19.3 0.7 103 7.5 8.3 43 52

Table 4. Summary of selected physical properties and alkalinity results, Voyageurs National Park, Minnesota, 2001-03. 

[Measurements shown here are those recorded at the Secchi depth; °C, degrees Celsius; m, meters; μS/cm; microsiemens per centimeter; mg/L, milligrams per 

liter]

Water-quality results 11
12 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

(Payne, 1991). The concentrations of phosphorus in Black 

Bay were generally greater in 2003 than in 2001 and 2002. 

Total phosphorus concentrations at Rainy Lake at Black Bay 

(west) near International Falls (Site 44) on July 7, 2003 and 

September 28, 2003 contribute to this pattern (table 10, appendix). Because Black Bay is shallow, bottom sediments are 

frequently stirred up from wind action and motorboat activity. With the low water levels in 2003, this bottom sediment 

stirring probably was accentuated and account for increased 

phosphorus concentrations. Total phosphorus concentrations at Kabetogama Lake in 2003, however, generally were 

lower than in 2001 and 2002. By combining the 3 sites in 

Kabetogama Lake, the mean spring (May samples only) total 

phosphorus concentration was 0.020 mg/L.

Similar to total phosphorus, mean total ammonia plus 

organic nitrogen concentrations were greater in Black Bay and 

Kabetogama Lake than in Sand Point, Namakan, and Rainy 

Lakes (table 5). In general, all sites showed greater total 

ammonia plus organic nitrogen concentrations in August than 

in May. Nitrite plus nitrate nitrogen concentrations greatly 

varied in all the lakes and were greatest in lakes having low 

total phosphorus concentrations (Sand Point, Namakan, and 

Rainy). Lower mean nitrite plus nitrate nitrogen concentrations in Black Bay and Kabetogama Lake corresponded to 

greater mean total phosphorus concentrations. This may be the 

result of greater utilization of nitrate in the highly productive 

lakes. Nitrite plus nitrate nitrogen concentrations were below 

detection limits in several samples from Kabetogama Lake and 

Black Bay, indicating that utilization was great (Payne, 1991).

Algal Productivity

Chlorophyll is a colored pigment in plants that absorbs 

light energy (Coleman and Dewar, 1997). During photosynthesis, carbohydrates are formed from water and carbon 

dioxide under the influence of sunlight and chlorophyll. These 

��������������������

����������������

����������������������������

�����������������

�����������������������

�������������

�����������������������

����

����

�

����

����

��

��

��

�

�

��

��

��

������������������������

����������������������

�������

�

�

�

�

�

�

����������������

��������

��������

��������

���������

���������

����������������

��������

��������

��������

���������

���������

����������������

��������

��������

��������

���������

���������

�����������

������������������������

�������������������

����������������������������������������

�����������������������

����������������������

�����������������������������������������������

Figure 4. Monthly data for (a) Secchi-disk transparency, (b) total phosphorus, and (c) chlorophyll-a
Dissolved nitrite plus 

nitrate nitrogen

Dissolved ammonia 

plus organic nitrogen

Total ammonia plus 

organic nitrogen

Total

 phosphorus

Dissolved 

phosphorus

Sand Point Lake below Harrison Narrows near Crane Lake, Site 7

minimum <0.022 0.41 0.49 0.012 0.006

maximum 0.143 0.63 0.63 0.021 0.012

mean 0.056 0.48 0.56 0.018 0.010

median 0.046 0.44 0.58 0.020 0.011

Namakan Lake near Ray, Site 14 

minimum 0.038 0.32 0.38 0.008 0.003

maximum 0.092 0.35 0.53 0.028 0.005

mean 0.057 0.33 0.44 0.016 0.004

median 0.055 0.33 0.44 0.014 0.005

Rainy Lake at Brule Narrows near International Falls, Site 5

minimum 0.040 0.30 0.37 0.011 0.003

maximum 0.094 0.34 0.37 0.038 0.006

mean 0.066 0.31 0.37 0.018 0.005

median 0.056 0.31 0.37 0.013 0.005

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11

minimum <0.005 0.37 0.48 0.013 0.007

maximum 0.035 0.52 0.78 0.063 0.018

mean -- 0.43 0.65 0.030 0.011

median -- 0.42 0.66 0.026 0.010

Kabetogama Lake at Cemetary Island near Ray, Site 43 

minimum <0.005 0.37 0.51 0.014 0.004

maximum <0.013 0.46 0.93 0.087 0.024

mean -- 0.41 0.64 0.040 0.010

median -- 0.39 0.54 0.035 0.007

Kabetogama Lake near Grave Island near Ray, Site 45 

minimum <0.005 0.39 0.49 0.012 0.004

maximum 0.037 0.46 1.10 0.082 0.020

mean -- 0.42 0.69 0.035 0.010

median -- 0.43 0.57 0.028 0.008

Rainy Lake at Black Bay Narrows near International Falls, Site 1

minimum <0.005 0.35 0.49 0.026 0.006

maximum 0.060 0.73 0.90 0.079 0.032

mean -- 0.53 0.73 0.044 0.016

median -- 0.49 0.69 0.043 0.011

Rainy Lake at Black Bay near International Falls, Site 16 

minimum <0.005 0.36 0.46 0.023 0.006

maximum 0.057 0.54 1.10 0.104 0.021

mean -- 0.44 0.74 0.054 0.012

median -- 0.44 0.72 0.049 0.011

Rainy Lake at Black Bay (West) near International Falls, Site 44

minimum <0.013 0.47 0.65 0.029 0.011

maximum 0.064 0.77 1.10 0.230 0.027

mean 0.019 0.62 0.83 0.062 0.018

median 0.008 0.64 0.83 0.057 0.015

Table 5. Summary of selected nutrient analytical results, Voyageurs National Park, Minnesota, 2001-03

[all units in milligrams per liter; <, less than; --not determined]

Water-quality results 13
14 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

carbohydrates undergo a series of complex reactions to form 

the compounds of which plant biomass is made. Chlorophyll-a 

concentrations can be a simple indicator of algal biomass in 

surface water.

Chlorophyll-a varies seasonally (fig. 4c) with peak 

concentrations normally occurring in late summer. Sites in 

Sand Point, Namakan, and Rainy Lakes maintained low chlorophyll-a concentrations from 2001 through 2003. Chlorophyll-a concentrations at these sites never exceeded 6 mg/L. 

Kabetogama Lake and Black Bay had greater chlorophyll-a 

concentrations and more pronounced seasonal variation than 

the Sand Point, Namakan, and Rainy sites. The range in chlorophyll-a concentrations in Kabetogama Lake was less than 

0.1 to an estimated 67.3 mg/L, and the range in Black Bay was 

an estimated 0.7 to 47.8 mg/L (table 6).

Peaks in chlorophyll concentrations generally occurred 

in late summer. In Black Bay and Kabetogama Lake, concentrations were greater in 2002 than 2001 and a second peak 

concentration occurred in mid to late September 2002. It is 

important to note that samples were not collected on the same 

day each year and much of the uncertainty in annual changes 

of chlorophyll concentrations may be associated with sampling date (Hanna and Peters, 1991).

During 2003, chlorophyll-a concentrations generally were lower at all sites and were substantially lower at 

Black Bay and Kabetogama Lake. Also during 2003, Black 

Bay experienced its peak concentration at the beginning of 

August, with much lower concentrations in September. At 

Kabetogama Lake, however, the peak concentration occurred 

in mid-September. Low chlorophyll-a concentrations in 

September in Black Bay may have resulted from less nutrient 

rich water from Kabetogama Lake that was flowing through 

Gold Portage and into Black Bay during late summer, as it had 

in the previous 2 years (fig. 3). This can be explained by the 

low water levels in 2003 and the beaver dam at Gold Portage, 

described previously.

Trophic State Indicators

Federal requirements for “fishable” and “swimmable” 

waters have resulted in numerous efforts to classify a lake’s 

trophic state (Carlson and Simpson, 1996). Nutrient and chlorophyll-a concentration data along with transparency measurements normally are used in these classification systems. 

Trophic State Indices (TSI) were computed using equations 

developed by Carlson (1977). The indices are computed 

from measurements of Secchi-disk transparency or results of 

analyses for chlorophyll-a or total phosphorus. Carlson’s index 

is a numeric scale that represents the amount of algal biomass 

in surface waters and the range of the index is approximately 

0-100 (but, theoretically, the index has no limit). Each 10-unit 

increment in the scale represents a doubling of algal biomass 

in surface waters.

The significance of the TSI is that it is a simple numeric 

index that can be related to the traditional typological scheme 

Sand Point Lake below Harrison Narrows near Crane Lake, Site 7

minimum 0.2

maximum 3.0

mean 1.7

median 2.1

Namakan Lake near Ray, Site 14 

minimum 0.5

maximum 2.1

mean 1.6

median 1.9

Rainy Lake at Brule Narrows near International Falls, Site 5

minimum 1.0

maximum 3.6

mean 1.6

median 1.1

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11

minimum 0.8

maximum 31.2

mean 5.8

median 3.0

Kabetogama Lake at Cemetary Island near Ray, Site 43 

minimum 0.4

maximum 23.7

mean 5.7

median 3.5

Kabetogama Lake near Grave Island near Ray, Site 45 

minimum <0.1

maximum 67.3

mean 7.7

median 3.5

Rainy Lake at Black Bay Narrows near International Falls, Site 1

minimum 1.0

maximum 14.9

mean 5.0

median 3.6

Rainy Lake at Black Bay near International Falls, Site 16 

minimum 0.9

maximum 27.2

mean 6.5

median 3.5

Rainy Lake at Black Bay (West) near International Falls, Site 44

minimum 0.7

maximum 47.8

mean 6.0

median 3.2

Table 6. Summary of chlorophyll-a analytical results, Voyageurs 

National Park, Minnesota, 2001-03

[all units in micrograms per liter]
of Nauman (1919). Unlike the typological index, Carlson’s 

index represents a continuum of trophic state, and not simply 

the four traditional lake types (oligotrophic, mesotrophic, 

eutrophic, and hypereutrophic). The continuum may be more 

useful for assessing the change of lake trophic state through 

time and comparing between lakes that are very similar.

An evaluation of TSI calculated from data collected during the baseline study (Payne, 1991) found that TSI computed from chlorophyll-a concentrations (TSI CHY) might 

be preferable to TSI values computed from total phosphorus 

concentrations (TSI TP) because data from lakes in Voyageurs 

National Park at times does not match Carlson’s regression 

that relates chlorophyll-a to phosphorus. Soluble organic substances that color some of the Park’s water bodies affect the 

indices computed from Secchi-disk transparency (TSI SD).

The sampling schedule for this study resulted in about 

12 sets of samples for each site in Black Bay and Kabetogama 

Lake during each May-October sampling season. TSI CHY 

values ranged from 9 to 71 during the 2001-03 study, with the 

exception of one sample collected at Kabetogama Lake during 

2001, in which the chlorophyll-a value was less than 1. For 

that sample a value of one-half the minimum reporting limit 

(MRL) was used to compute the TSI CHY means. Values for 

Black Bay ranged from 27 to 68, whereas Kabetogama Lake 

had the maximum TSI CHY value of 71 on September 30, 

2002. Biweekly samples collected at Sand Point, Namakan, 

and Rainy Lakes were analyzed by NRRI (table 12, appendix). 

Because of potential variability among different laboratories, 

caution should be exercised when comparing TSI values at 

these reference sites with Kabetogama and Black Bay (for 

which biweekly chlorophyll-a samples were analyzed by the 

NWQL). In general, the TSI values for Sand Point, Namakan, 

and Rainy Lakes were lower, ranging from 9 to 47.

Sand Point, Namakan, and Rainy Lakes all had mean TSI 

CHY values (2001-03) of 33-34. The mean value for Black 

Bay was 44 and the mean value for Kabetogama Lake was 43. 

Based on these values, these lakes would be considered oligotrophic to mesotrophic. Using mean lake values, Kabetogama 

Lake and Black Bay would be considered mesotrophic; however individual TSI CHY values would classify these water 

bodies as eutrophic during the late summer. 

Effects on Water Quality and Trophic 

State

Historical climate and hydrologic conditions 

Total ammonia plus organic nitrogen, total phosphorus, 

dissolved phosphorus, chlorophyll-a, and trophic state indices 

were compared between the 2001-03 study period and the 

baseline study (1977-84). Changes between the two may be 

due not only to changes in lake outflows (and ultimately the 

new rule curves), but possibly due to historical hydrologic and 

climate conditions. 

Monthly mean air temperatures at the International Falls 

weather station for May through September from 2001 to 2003 

exceeded the mean temperatures for May through September 

1948 to 2003 in 11 of the 15 months (National Oceanic and 

Atmospheric Administration, 2003). The warmer air temperatures for 2001 to 2003 extended the warming trend that started 

in 1980 (Kallemeyn and others, 2003). Climate conditions during the baseline study were more variable than 2001–03 with 

1977, 1980, 1981, and 1983 being above average temperature 

years and 1978, 1979, and 1982 being below average years. 

Accumulated degree days less than 10 degrees Celsius (oC) in 

the water column for the surface to 10 m depth zone (epilimnion) for the summer and early fall of 2001 to 2003, which are 

positively correlated with air degree days, generally exceeded 

long-term mean values (Kallemeyn and others, 2003). Accumulated degree days in Kabetogama and Rainy Lakes were 

greater than the long-term mean in all 3 years. In Namakan 

Lake, the accumulated degree days from 2001 and 2002 

exceeded the long-term mean, whereas the 2003 value was 

slightly less than the long-term mean. The 2001 accumulated 

degree days for Sand Point Lake also exceeded the long-term 

mean, but in 2002 and 2003 the accumulated degree-days were 

about 35 units below the long-term mean. The accumulated 

degree-days in the water column in 2001 were the greatest that 

has been recorded in the last 23 years in all the lake basins 

except Kabetogama Lake, where it was the fourth greatest. 

During the period from 1948 to 2002 there has been a 

downward trend in precipitation of about –0.79 cm (–0.31 

inches) per decade (Kallemeyn and others, 2003). During the 

baseline study, 4 years had below average precipitation, and 

4 years had above average precipitation. Total annual precipitation was above average in 2001, slightly below average 

in 2002 (Kallemeyn and others, 2003), and below average 

in 2003. Although 2002 had below average precipitation, 

Rainy Lake and Rainy River (west of the study area in fig. 1) 

experienced very high water levels and flows during the late 

spring and summer of 2002 (International Rainy Lake Board 

of Control and International Rainy River Water Pollution 

Board, 2002). The 2002 peak level on Rainy Lake was the 

highest since 1950 (International Rainy Lake Board of Control 

and International Rainy River Water Pollution Board, 2002), 

due to extreme rainfall events that occurred in June. Average 

inflow from the Namakan River (which supplies most of the 

water to Namakan Reservoir) during 1977-84 was 114 m3

/s 

(about 4,024 ft3/s). During the current study average flow was 

94 m3/s. 

Comparison with pre-rule curve changes 

Numerous studies have been conducted to serve as a 

baseline to compare to the post-2000 rule curve samples 

collected from the lakes in Voyageurs National Park. Hargis 

(1981) measured chlorophyll-a concentrations in the sumEffects on water quality and trophic state 15
16 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

mer of 1979. Keppner and Stottlemeyer (1988) converted the 

Hargis data to lakewide means and compared it to their own 

data collected in 1985 and 1986. Payne (1991) reported on 

samples collected in 1977-84 and again in July 1999 (Payne, 

2000). The baseline data mostly were collected during May 

and August, therefore May and August data from the current 

study were compared to seasonal means to document change 

that may have occurred in the first years following the January 

2000 implementation of the new rules for reservoir operation.

 May and August data from the current study and the 

baseline study (Payne, 1991) are compared in figure 5. For 

each site a minimum of five data points per study were used 

for comparison. Because not all sites were sampled during the 

baseline study, Kabetogama Lake is evaluated with data from 

Site 11, and Black Bay is evaluated with data from Site 16. 

The results were mixed for median total ammonia plus 

organic nitrogen concentrations. For some lakes there was 

a slight increase from baseline to 2001-03 (Sand Point and 

Kabetogama Lakes), a slight decrease (Namakan Lake and 

Black Bay), or almost no change (Rainy Lake). Rank sum 

tests (Helsel and Hirsch, 1992) performed on the nitrogen 

data showed no significant differences in mean ammonia plus 

organic nitrogen concentrations between the baseline and 

2001-03 data sets. 

All sites had greater median total phosphorus concentrations during 2001-03 than during the baseline study (fig. 

5). Rank sum tests performed on the total phosphorus data 

showed no significant differences between mean concentrations between the baseline study and the 2001-03 study. 

Median dissolved phosphorus results were mixed. For Sand 

Point Lake there was an increase in the median concentration, 

Namakan Lake and Black Bay had a decrease in median concentration, and Rainy and Kabetogama Lakes had little change 

(fig. 5). 

All median chlorophyll-a concentrations (and median TSI 

CHY values) were lower in 2001-03 than during the baseline 

study. Decreases between the baseline and 2001-03 chlorophyll-a and TSI CHY mean values in Kabetogama Lake and 

Black Bay were significant (p=0.021 and p=0.007, respectively).

Because the inflows to the reservoirs (Namakan and Vermillion Rivers) were not sampled during the current study, it 

is impossible to say whether phosphorus loading has increased 

or decreased. It is possible that a substantial amount of total 

phosphorus in the lakes is being recycled from internal sources 

(lake sediments) rather than external sources (inflows from 

Namakan and Vermillion Rivers).

Decreased TSI CHY values indicate a decreased algal 

biomass. This decrease in algal biomass also was reflected 

in slightly deeper Secchi-disk transparency. For example, the 

mean Secchi-disk transparency in Black Bay (Site 16) during 

the baseline study was 0.82 m (Payne, 1991, p. 28), whereas 

during the current study the mean was 0.94 m. A decrease 

in algal biomass normally is a response to decreased nutrient concentrations, particularly phosphorus, in lakes where 

phosphorus is a limiting nutrient; however, median total phosphorus concentrations did not decrease between the two study 

periods. Not only were the median values for chlorophyll-a 

and TSI CHY lower, but also the range in the data was smaller 

for most of the sites. This is particularly noticeable in Kabetogama Lake and Black Bay (fig. 5).

The results of the current study (2001-03) generally are 

similar to results of the interim USGS study (Payne, 2000), 

which compared the water quality of samples collected in July 

1999 to samples collected during the baseline study. Between 

the baseline study and 1999 significant differences were 

observed in total phosphorus, chlorophyll-a, and Secchi disk 

transparency (Payne, 2000). Total phosphorus and total ammonia plus organic nitrogen concentrations in 1999 were lower 

than the baseline study in Black Bay and Kabetogama Lake. 

Median chlorophyll-a concentrations at Kabetogama Lake and 

Black Bay were about 10 percent less than the baseline study 

median values. This decrease in algal biomass was evident 

from the increase in 1999 Secchi-disk transparency values at 

Black Bay and Kabetogama Lake. These changes were consistent with the monitoring data presented by Kallemeyn and 

others (2003). 

Results of the current study (2001-03) were compared to 

the results of the previous USGS studies to minimize variability of results due to differences in site location, laboratory, and 

field methods. Results also were compared to Hargis (1981) 

and Kepner and Stottlemyer (1988) because the USGS studies 

were not continuous. The compilation of these shorter term 

data sets produced a more continuous set of data, reducing the 

likelihood of only evaluating data sampled during extreme or 

unusual hydrologic events. For this same reason, continued 

monitoring of the trophic status may be necessary to document changes resulting from the 2000 rule curve change. The 

samples from other studies were collected at different sites 

on these lakes and chlorophyll-a concentrations can be quite 

variable throughout a large water body, therefore some of 

the differences in results may be due to spatial variability. In 

addition, the TSI values presented in Kepner and Stottlemyer 

(1988) made no distinction between Rainy Lake and Black 

Bay. To limit the variability due to timing of sample collection, 

only August values are compared in table 7. 

All major lakes in the Park experienced lower TSI CHY 

values during 2001-03 than during any of the previous studies. TSI CHY values at Sand Point Lake in 2001-03 were 

34 percent lower than the combined mean of the previous 

studies. TSI CHY values at Namakan Lake were 24 percent 

lower, and TSI CHY values at Kabetogama were 13 percent 

lower than the previous studies. Although Rainy Lake was not 

distinguished from Black Bay in the Hargis (1981) study or in 

the Kepner and Stottlemyer (1988) study, combined 2001-03 

Rainy Lake and Black Bay values were 21 percent lower than 

the mean reported values from 1979 to 1986. Rainy Lake and 

Black Bay TSI CHY values were 31 percent and 20 percent 

lower, respectively, in 2001-03 than during the USGS baseline 

study.

Because line graphs and boxplots are ways of visualizing data and are not statistical tests, a Kendall’s tau trend test 
������������������

��������������������

������������������������

��� �������������

�����������������������

��������������������������

��������������������������������

�����������������

�����������������������

���������������������

�����������������������

��������������

�����������������������

�������������������

����

����

����

�

����

����

����

����

����

�

����

����

����

����

�

����

����

���

����

�

����

����

����

����

�

����

�������

�������

�������

�������

�������

�������

�������

�������

�������

�������

��������������� ������������ ���������� ��������������� ���������

�����������

������������������������

��������������������������

��������������������������

�������

�������

����

����

������

����

����

Figure 5. Boxplots comparing historical baseline concentrations to 2001-03 for (a) total ammonia plus organic nitrogen, (b) total phosphorus, (c) dissolved phosphorus, (d) chlorophyll-a , and (e) trophic state index. 

Effects on water quality and trophic state 17
18 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

(Kendall, 1975) was performed on the data. Tau is a measure 

of the strength of the monotonic association between two 

variables, whereas the probability (p-value) is the likelihood 

of obtaining the test statistic (tau). Kendall’s tau was chosen 

for a variety of reasons. Kendall’s tau is a nonparametric trend 

test that is rank based and, therefore, resistant to the effects of 

extreme values and to deviations from a linear relation (Hirsch 

and others, 1993). All monthly sample sets had between 7 

and 13 values and Kendall’s tau may be more appropriate 

than other trend tests for sample sizes less than 20 (Helsel and 

Hirsch, 1992). 

To eliminate interlaboratory variability, only data from 

the NWQL were used, and to eliminate seasonal variability, 

the trend test was performed separately on May and August 

data. Algal productivity is highly seasonal, thus comparing a May value to an August value does not contribute any 

information about the existence of a trend (Smith and others, 

1982). Samples collected in June, July, and September were 

not included because samples were not collected during these 

months in the baseline study. Including these data could lead 

to false trends for 2001-03. 

Separating May and August values also revealed patterns 

in the data. While, there were positive trends (increasing concentrations) in total phosphorus for all the sites during May, 

none were significant (having a probability value of less than 

0.05). For the August samples, the only site showing a trend 

was Sand Point Lake, which had a significant negative trend 

(decreasing concentrations) in total phosphorus (tau=-0.56, 

probability=0.03). 

Results of trend tests for TSI CHY were the same as 

those for chlorophyll-a, because the TSI is based on the chlorophyll-a value. Any differences between the tau are due to 

rounding. There were negative trends in TSI CHY (and chlorophyll-a) at all sites during May. However, the only significant 

trend was at Kabetogama Lake (tau=-0.42, probability=0.05). 

None of the sites had significant trends in August. 

Comparison of Kabetogama Lake and Black Bay 

with other lakes

Lower nutrient concentrations, lower chlorophyll-a 

concentrations, and lower trophic state indices were measured 

in Sand Point, Namakan, and Rainy Lakes, near the eastern 

and northern boundaries of the Park than in Kabetogama Lake 

and Black Bay (fig. 5). Kabetogama Lake and Black Bay, 

located at the southern and western boundaries of the Park, not 

only had greater (mean and median, tables 5 and 6) nutrient 

and chlorophyll concentrations, and trophic indices, but also 

generally had greater alkalinities, greater dissolved solids 

concentrations, and lower Secchi-disk transparencies (table 4). 

The differences between Kabetogama Lake and Black Bay and 

the other lakes during the current study were similar to those 

found during the baseline USGS study (Payne, 1991) and during the interim USGS study (Payne, 2000). 

Although water-quality samples were not collected from 

Namakan River as part of the current study, Payne (1991) 

reports that the water quality of the three lakes along the 

eastern and northern boundary were similar to those of the 

Namakan River—the major source of inflow that drains an 

extensive area of exposed bedrock and thin noncalcareous 

glacial sediments east of the Park. The soil in this area is relatively shallow, has a thin layer of forest litter, and is strongly 

acidic (Kepner and Stottlemyer, 1988). If the soil material is 

derived from granite, it also is typically low in nutrients (Kallemeyn and others, 2003). Kabetogama Lake and Black Bay 

receive inflow from two streams that drain an area that is overlain by calcareous drift south and west of the Park. These soils 

have clay loam sub-layers and are poorly drained (Kepner and 

Stottlemyer, 1988). Kabetogama Lake has greater concentrations of nutrients in inflows than the Park’s other large lakes 

(Payne, 1991) presumably because the sediments flowing into 

Kabetogama Lake are unusually rich in nutrients.

Not only is the source of the inflows important to water 

quality, but also the depth and circulation of the lakes are 

important. Sand Point, Namakan, and Rainy Lakes are deeper 

and have dimictic circulation (the lake water mixes twice per 

year during spring and fall turnover), whereas Kabetogama 

Lake and Black Bay are shallower and have polymictic circuLake 1979 (as reported 

by Hargis, 1981)

1985 ( as reported by 

Kepner and 

Stottlemeyer, 1988)

1986 (as reported by 

Kepner and 

Stottlemeyer, 1988)

1979-83 (as reported 

by Payne, 1991)

2001-03 Current 

study 

Sand Point Lake 46 54 45 36 30

Namakan Lake 44 41 46 35 32

Rainy Lake 53 43 46 39 27

Kabetogama Lake 65 58 64 58 53

Black Bay -- -- -- 60 48

Table 7. Comparison of mean August trophic state values based on chlorophyll-a analysis for major lakes and bays in Voyageurs 

National Park, Minnesota 

[ --, not determined]
lation (mixing many times per year). The shallow water bodies 

experienced seasonal increases in nutrient concentrations that 

did not occur in the deeper lakes. This indicates a possible 

link between the frequent recirculation of these lakes and the 

internal recycling of phosphorus (Payne, 1991). 

Comparison of the extent of the changes in water quality shows that changes in Kabetogama Lake and Black Bay 

were greater than the other lakes. In particular, differences in 

median chlorophyll-a concentration and trophic state index 

were greater in Kabetogama and Black Bay than in Sand 

Point, Namakan, and Rainy Lake. This also was evident from 

the significant decreases in mean chlorophyll-a and TSI CHY 

values for Kabetogama Lake and Black Bay.

Continued monitoring of the trophic status of the lakes 

and bays may be necessary to determine if changes in water 

quality are due to changes in water-level fluctuation. The 

data collected while the IJC’s 2000 rule curves are in effect 

will serve as a baseline for any future changes in lake level 

management. Some alternatives for future monitoring include 

monthly sampling for total phosphorus and chlorophyll-a, 

monthly monitoring of physical properties, and monitoring 

inflows and outflows throughout the summer. Monitoring 

inflows and outflows may include the use of water-quality 

monitors to measure physical properties, and total phosphorus. 

Continued sampling during May and August would be one 

alternative for ensuring a continuum in the data set, given the 

historic emphasis on the collection of May and August total 

phosphorus and chlorophyll-a samples. Continued sampling 

may be important because the hydrologic events during the 

2001-03 study were extreme and monitoring for water-quality 

changes over long periods of time could reduce the possibility 

of sampling only during extraordinary hydrologic conditions. 

Long-term sampling also is useful in making decisions concerning lake management. 

Summary

Implementation of an order by the International Joint 

Commission in January 2000 has changed operating procedures for dams that regulate Rainy Lake and Namakan 

Reservoir, two large reservoirs in Voyageurs National Park in 

northern Minnesota. These new procedures were expected to 

restore a more natural water regime and affect water levels, 

water quality, and trophic state. Water-quality samples were 

collected from May 2001 through September 2003 from sites 

in Rainy Lake, including Black Bay, and Namakan Reservoir, 

which consists of five inter-connected lakes, including Sand 

Point, Namakan, and Kabetogama. Results of laboratory 

analysis and field measurements of chemical and physical 

properties were compared to baseline data collected prior to 

the change in operating procedures.

Due to the unusually excessive precipitation events in 

2001 and 2002, and the drought conditions in 2003, Rainy and 

Namakan Reservoir levels exceeded the bounds of the 2000 

rule curve during all 3 years of the study. Given that the IJC’s 

rule curves were not adhered to, attempts to determine whether 

water quality and trophic state have been affected by the rule 

change has been difficult. Changes in the timing of peak lakesurface elevations in Namakan Reservoir were not as substantial as expected. Peak lake-surface elevation occurred earlier 

in 2001, but occurred later than predicted (late June to early 

July) in 2002, and much later than predicted in 2003. Operation of Namakan Reservoir under the new rule curve and local 

hydrologic conditions resulted in an increase in the number 

of days that water flowed through Gold Portage in 2001 and 

2002; however, incidence of flow was 227 days in 2003, well 

below the value expected if operating within the limits of the 

new rule curve. 

The changes in water management rules also were 

expected to lower phosphorus loading in Namakan Reservoir, 

and especially in Kabetogama Lake. The median total phosphorus concentration, however, increased slightly in Kabetogama Lake (as well as all the other major lakes and bays) 

between 1977-84 (the U.S. Geological Survey baseline study) 

and 2001-03. Because the inflows to the reservoirs (Namakan 

and Vermillion Rivers) were not sampled during the current 

study, it is not possible to conclude whether phosphorus loading has increased or decreased. It is possible that a substantial 

amount of total phosphorus in the lakes is being recycled from 

internal sources (lake sediments) rather than external sources 

(inflows from Namakan and Vermillion Rivers). Kendall’s tau 

trend tests were calculated for all sites. To eliminate seasonal 

variability, the trend test was performed separately on May 

and August data. No sites had significant increasing May 

or August trends. August total phosphorus values showed a 

significant decreasing trend (tau=-0.56, probability=0.03) for 

Sand Point Lake. 

Changes in productivity and nutrient enrichment, relative 

to baseline data, also were examined. Sand Point, Namakan, 

and Rainy Lakes all had mean trophic state index (TSI CHY) 

values (May through October 2001-03) of 33-34. The mean 

value for Black Bay was 44 and the mean value for Kabetogama Lake was 43. Given the TSIs calculated for the Voyageurs Lakes from 2001-03, Sand Point, Namakan, and Rainy 

Lakes would be considered oligotrophic to mesotrophic, and 

Kabetogama and Black Bay would be considered mesotrophic. 

TSI CHY values at Kabetogama were 13 percent lower than 

the previous studies. Two previous studies made no distinction 

between Rainy Lake and Black Bay. Therefore 2001-03 data 

from Rainy Lake and Black Bay was combined for comparison. Combined 2001-03 Rainy Lake and Black Bay TSI 

CHY values were 21 percent lower than the mean reported 

values from 1979–1986. Comparison of Rainy and Black Bay 

individually, showed that 2001-03 TSI CHY values were 31 

percent and 20 percent lower, respectively than during the 

baseline study. Mean and median chlorophyll-a concentration 

decreased in all lakes and bays between the baseline study and 

the current study. Rank sum tests showed that the decreases in 

mean concentration between the baseline and 2001-03 study 

were significant for Kabetogama Lake (p=0.021) and Black 

Summary 19
20 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Bay (p=0.007). However, Kendall’s tau trend tests for May and 

August data, showed no significant positive or negative trends 

in chlorophyll-a or TSI CHY, with the exception of the May 

chlorophyll-a and TSI CHY values which had a significant 

negative trend (tau=-0.42, probability=0.05) for Kabetogama 

Lake. 

One of the objectives of the report was to examine 

whether the changes in Kabetogama Lake and Black Bay were 

greater than the changes in Sand Point, Namakan, and Rainy 

Lakes. Changes in median concentration for some constituents 

were greater in Black Bay and Kabetogama Lake compared to 

the other three lakes (chlorophyll-a and TSI CHY), whereas 

changes in median concentrations for other constituents 

(for example, total ammonia plus organic nitrogen and total 

phosphorus) were similar to the other three lakes. The range 

in the data (minimum to maximum chlorophyll-a concentrations and trophic state indices) was noticeably smaller in 

2001-03 compared to baseline in Black Bay and Kabetogama 

Lake, whereas the ranges in other lakes decrease. In addition, the oligotrophic to mesotrophic classification of Sand 

Point, Namakan, and Rainy Lakes did not change between the 

baseline and current studies. In contrast, Kabetogama Lake 

and Black Bay were classified as eutrophic during the baseline study; based on 2001-03 data, they would be considered 

mesotrophic. 

Changes in water quality of the lakes in Voyageurs 

National Park may be due to changes in water level fluctuation. However, given the extreme hydrologic conditions during 2001-03 study, continued monitoring of the trophic status 

of the lakes and bays may be necessary. The water-quality 

monitoring collected while the IJC’s 2000 rule curves are in 

effect will serve as a baseline for any future changes in lake 

level management. In addition to continued monitoring, some 

alternatives include monthly sampling for total phosphorus 

and chlorophyll-a, monthly monitoring of physical properties, 

and monitoring inflows and outflows throughout the summer. 

Due to the historic emphasis on the collection of May and 

August total phosphorus and chlorophyll-a samples, continued 

sampling during May and August would be one alternative for 

ensuring a continuum in the data set. Monitoring for waterquality changes over long periods of time could reduce the 

possibility of sampling only during extraordinary hydrologic 

extremes and are useful in making informed lake management 

decisions.

References 

Carlson, R.E., 1977, A trophic state index for lakes: Limnology and Oceanography, v. 22, no. 2, p. 361-369.

Carlson, R.E., and Simpson, J., 1996, A coordinator’s guide to 

volunteer lake monitoring methods: North American Lake 

Management Society, 96 p. 

Coleman, G.J., and Dewar, David, 1997, The Addison-Wesley 

Science Handbook: Ontario, Addison-Wesley Publishers 

Limited, 281 p.

Hanna, Micheline, and Peters, R.H., 1991, Effect of sampling protocol on estimates of phosphorus and chlorophyll 

concentrations in lakes of low to moderate trophic status: 

Canadian Journal of Fisheries and Aquatic Science, vol. 48, 

p. 1979-1986.

Hargis, J.R., 1981, Ecological analysis of the plankton communities of Voyageurs National Park: Final Report, National 

Park Service contract no. CX-6000-8-R133, University of 

Minnesota-Duluth, 47 p.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: Amsterdam, Elsevier Science Publishers, 

522 p. 

Hirsch, R.M., Helsel, D.R., Cohn, T.A., and Gilroy, E.J., 1993, 

Statistical analysis of hydrologic data, in Maidment, D.R., 

ed., Handbook of hydrology: New York, McGraw-Hill, Inc., 

p. 17.1-17.55.

International Rainy Lake Board of Control and International 

Lake of the Woods Control Board, 1984, Briefing paper 

submitted to the International Joint Commission: Winnipeg, 

Canada, 41 p. 

International Rainy Lake Board of Control and International 

Rainy River Water Pollution Board, 2002, Joint Annual 

Report for January 2001 to September 2002: as submitted 

to the International Joint Commission on October 31, 2002, 

Ottawa, Ontario, Canada and Washington, D.C., 25 p. 

Kallemeyn, L.W., 2000, Proceedings of the Rainy Lake–

Namakan Reservoir ecological monitoring workshop, 

International Falls, Minn., January 11-12, 2000. Report to: 

International Joint Commission, Washington, DC, 60 p.

Kallemeyn, L.W., Holmberg, K.L., Perry, J.A., and Odde, 

B.Y., 2003, Aquatic synthesis for Voyageurs National Park: 

U.S. Geological Survey Biological Resources Division 

Information and Technology Report 2003-0001, 96 p.

Kendall, M.G., 1975, Rank Correlation Methods, 4th ed.: London, Charles Griffin, 202 p.

Kepner, R., and Stottlemyer, R., 1988, Physical and chemical factors affecting primary production in the Voyageurs 

National Park system: Great Lakes Area Resource Studies 

Unit Technical Report 29, Michigan Technological University, Houghton, 82 p.

Lake of the Woods Control Board, 2004, Winnipeg River 

Drainage Basin Data, accessed January 2004 at http://www.

lwcb.ca/water-flowdata
National Oceanic and Atmospheric Administration, 2003, 

Local climatological data, annual summary with comparative data, International Falls, Minnesota: U.S. Department 

of Commerce, National Climatic Center, Ashville, N.C., 

4 p. 

Naumann, E.C.L., 1919, Some aspects of the ecology of the 

limnoplankton, with special references to the phytoplankton: Svensk Botanisk Tidskrift, v. 13 no. 2, p. 129-163.

Payne, G.A., 1991, Water quality of lakes and streams in 

Voyageurs National Park, northern Minnesota, 1977-84: U.S. 

Geological Survey Water-Resources Investigations Report 

88-4016, 95 p.

Payne, G.A., 2000, Water quality of lakes in Voyageurs National 

Park, northern Minnesota, 1999: U.S. Geological Survey 

Water-Resources Investigations Report 00-4281, 12 p. 

Smith, R.A., Hirsch, R.M., and Slack, J.R., 1982, A study of 

trends in total phosphorus measurements at NASQAN stations: U.S. Geological Survey Water-Supply Paper 2190, 

34 p. 

Taylor, J.K., 1987, Quality assurance of chemical measurements: Chelsea, Michigan, Lewis Publishers, 328 p.

U.S. Environmental Protection Agency, 1986, Quality criteria 

for water 1986: Washington, D.C., Office of Water Regulations and Standards, EPA-440/5-86-001.

Wiche, G.J., Guttormson, K.G., Robinson, S.M., and Mitton, 

G.B., 2002, June 2002 floods in the Red River of the North 

Basin in Northeastern North Dakota and Northwestern Minnesota, U.S. Geological Survey Open-File Report 02-278, 

8 p.

References 21
22 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Appendix
Date 

Air 

Pressure 

(mm Hg)

Water 

Temperature 

(°C)

Secchi disk 

transparency (m)

Specific 

conductance, 

field (μS/cm)

Specific conductance, 

laboratory 

(μS/cm) Field pH

Laboratory 

pH

Dissolved 

oxygen 

(mg/L)

Total 

alkalinity 

as CaC03

(mg/L)

Bicarbonate alkalinity as HCO3 

(mg/L)

Carbonate 

alkalinity 

as CO3 

(mg/L)

Sand Point Lake below Harrison Narrows near Crane Lake, Site 7

5/16/01 -- 10.7 1.7 63 60 7.0 7.3 10.9 16 20 0

8/21/01 730 21.4 1.3 64 62 7.3 7.2 6.9 20 24 0

5/14/02 -- 4.9 1.6 82 -- 7.4 -- 11.8 -- -- --

8/21/02 730 19.1 2.3 55 -- 7.7 -- 9.9 -- -- --

5/14/03 -- 7.6 2.2 76 -- 7.2 -- 11.7 -- -- --

5/29/03 -- 14.8 1.9 66 -- 7.3 -- 11.5 21 25 0

6/10/03 -- 2.2 2.2 66 -- 7.1 -- 10.2 -- -- --

6/24/03 -- 20.6 2.9 67 -- 7.6 -- 8.8 -- -- --

7/23/03 -- 22.0 2.9 71 -- 7.5 -- 8.0 -- -- --

8/5/03 -- 23.6 3.3 72 -- 7.5 -- 7.7 -- -- --

8/19/03 -- 25.2 2.5 73 -- 7.7 -- 7.7 -- -- --

9/19/03 -- -- 3.3 -- -- -- -- -- -- -- --

9/29/03 -- 13.3 3.1 72 -- 7.1 -- 9.4 -- -- --

Namakan Lake near Ray, Site 14 

5/16/01 -- 9.9 2.1 50 46 7.2 7.6 10.7 14 17 0

8/21/01 731 22.1 2.3 48 49 7.3 7.9 7.8 16 20 0

5/14/02 -- 5.2 2.1 55 -- 7.2 -- 12.7 -- -- --

8/21/02 731 18.9 2.7 37 -- 7.4 -- 10.1 -- -- --

5/14/03 -- 5.9 3.0 55 -- 7.1 -- 12.0 -- -- --

5/29/03 -- 16.0 -- 46 -- 7.0 -- 12.4 16 20 0

6/10/03 -- 16.7 -- 46 -- 7.4 -- 10.4 -- -- --

6/24/03 -- 20.1 3.5 46 -- 7.6 -- 9.2 -- -- --

7/22/03 -- 21.9 3.0 48 -- 7.9 -- 8.2 -- -- --

8/5/03 -- 23.3 4.0 47 -- 7.2 -- 7.4 -- -- --

8/19/03 -- 25.3 3.0 48 -- 7.3 -- 7.7 -- -- --

9/19/03 -- 18.2 4.1 48 -- 6.7 -- 8.0 -- -- --

9/29/03 -- 13.6 3.5 49 -- 7.1 -- 9.0 -- -- --

Rainy Lake at Brule Narrows near International Falls, Site 5

5/15/01 -- 8.2 2.3 56 49 7.4 7.3 13.1 15 19 0

8/20/01 735 21.5 2.3 47 48 7.5 7.9 8.0 16 19 0

5/13/02 -- 6.2 2.3 64 -- 7.6 -- 12.9 -- -- --

8/20/02 -- 17.0 2.7 42 -- 8.2 -- 8.8 -- -- --

5/13/03 -- 10.5 2.2 52 -- 6.6 -- 12.1 -- -- --

5/28/03 -- 13.4 2.2 47 -- 7.1 -- 12.1 16 20 0

6/9/03 -- 15.9 2.0 44 -- -- -- 9.8 -- -- --

6/23/03 -- 19.0 2.8 46 -- 7.5 -- 9.3 -- -- --

7/21/03 -- 21.0 2.2 48 -- 7.7 -- 8.3 -- -- --

8/4/03 -- 22.1 2.5 47 -- 7.3 -- 7.8 -- -- --

8/18/03 -- 23.7 2.3 48 -- 6.8 -- 7.7 -- -- --

9/2/03 -- 19.2 2.5 48 -- 6.5 -- 7.8 -- -- --

9/15/03 -- 18.3 3.0 48 -- 7.1 -- 7.2 14 17 0

9/28/03 -- 12.1 3.0 48 -- 6.9 -- 9.2 15 19 0

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11

5/16/01 -- 8.0 2.1 102 -- 7.4 -- 9.3 35 42 0

Table 8. Physical properties and alkalinity results by site, Voyageurs National Park, Minnesota, 2001-03. 

[Water quallity measurements shown here are those recorded for samples from the Secchi depth; mm Hg, millimeters of mercury; °C, degrees Celsius; m, 

meters; μS/cm; microsiemens per centimeter; mg/L, milligrams per liter; --, not determined]

Appendix 23
24 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date 

Air 

Pressure 

(mm Hg)

Water 

Temperature 

(°C)

Secchi disk 

transparency (m)

Specific 

conductance, 

field (μS/cm)

Specific conductance, 

laboratory 

(μS/cm) Field pH

Laboratory 

pH

Dissolved 

oxygen 

(mg/L)

Total 

alkalinity 

as CaC03

(mg/L)

Bicarbonate alkalinity as HCO3 

(mg/L)

Carbonate 

alkalinity 

as CO3 

(mg/L)

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11—Continued

5/30/01 -- 14.8 -- 95 -- 7.4 -- 7.0 -- -- --

6/12/01 -- 18.2 2.5 94 -- 7.0 -- -- 36 43 0

6/25/01 -- -- 2.2 99 -- 7.7 -- 8.7 37 45 0

7/10/01 -- 22.5 2.1 98 -- 8.0 -- 8.6 51 62 0

7/24/01 -- 24.2 2.6 96 -- 7.4 -- 10.9 31 38 0

8/7/01 -- 26.8 1.3 97 -- 9.0 -- 9.9 35 43 --

8/21/01 731 22.9 1.2 100 99 8.6 7.8 9.5 42 52 --

9/5/01 -- 21.5 1.5 104 -- 7.7 -- 8.5 44 54 0

9/18/01 -- 19.0 2.5 98 -- 8.0 -- 7.1 56 68 0

10/2/01 -- 16.3 1.8 77 -- 7.6 -- 8.5 39 48 0

10/17/01 -- 11.3 2.0 80 -- 7.6 -- 8.6 41 50 0

5/14/02 -- 8.3 1.9 99 -- 7.3 -- 12.2 -- -- --

5/30/02 -- 13.9 2.1 62 -- 7.8 -- 4.7 22 27 0

6/12/02 -- 15.4 1.5 -- -- 7.2 -- -- -- -- --

6/26/02 -- 19.8 2.5 75 -- 8.1 -- 8.7 -- -- --

7/9/02 -- 23.6 1.5 118 -- 8.1 -- 9.2 -- -- --

7/23/02 -- 24.4 2.5 99 -- 8.2 -- 9.6 -- -- --

8/6/02 -- 22.3 1.8 90 -- 7.8 -- 8.3 -- -- --

8/21/02 731 20.4 1.4 80 -- 8.5 -- 11.7 -- -- --

9/5/02 -- 20.0 1.5 79 -- 7.9 -- 8.3 -- -- --

9/17/02 -- 20.5 1.5 78 -- 8.3 -- 9.8 -- -- --

9/30/02 -- 15.5 2.0 59 -- 7.6 -- 8.9 -- -- --

10/16/02 -- 9.9 2.8 57 -- 7.7 -- 10.1 -- -- --

5/14/03 -- 9.9 2.0 105 -- 7.4 -- 12.2 35 43 0

5/29/03 -- 15.7 1.8 90 -- 8.0 -- 11.9 40 49 0

6/10/03 -- 17.2 2.6 85 -- -- -- 9.7 -- -- --

6/24/03 -- 19.1 3.7 86 -- 7.7 -- 8.1 -- -- --

7/8/03 -- 20.6 3.2 86 -- 7.7 -- 8.4 -- -- --

7/22/03 -- 22.1 2.6 95 -- 8.3 -- 8.2 -- -- --

8/5/03 -- 23.3 2.7 98 -- 8.8 -- 8.5 -- -- --

8/19/03 -- 25.3 1.8 99 -- 9.2 -- 8.8 -- -- --

9/3/03 -- 20.6 1.4 97 -- 7.7 -- 7.2 -- -- --

9/17/03 -- 19.2 2.2 98 -- 7.7 -- 8.2 40 49 0

9/29/03 -- 14.0 2.1 97 -- 7.6 -- 8.9 39 48 0

Kabetogama Lake at Cemetary Island near Ray, Site 43 

5/17/01 -- 7.6 1.8 87 94 7.5 7.8 9.1 37 45 0

5/31/01 -- 13.6 2.7 94 -- 6.6 -- 7.1 -- -- --

6/12/01 -- 18.5 3.3 -- -- 7.5 -- -- -- -- --

6/26/01 -- 22.8 2.5 92 -- 7.4 -- 9.0 34 41 --

7/10/01 -- 19.8 2.5 94 -- 7.7 -- 9.5 34 41 0

7/24/01 -- 22.3 2.3 96 -- 7.9 -- 11.0 40 49 0

8/7/01 -- 25.2 1.6 93 -- 9.0 -- 8.8 55 67 --

8/22/01 731 22.2 1.2 97 93 9.0 8.8 10.0 38 46 3

9/5/01 -- 20.7 1.5 96 -- 7.9 -- 8.1 50 61 0

9/18/01 -- 17.9 1.5 98 -- 7.4 -- 9.1 40 49 0

10/2/01 -- 15.3 1.7 101 -- 7.6 -- 8.9 58 71 0

10/17/01 -- 10.0 2.3 99 -- 7.6 -- 8.7 40 48 0

Table 8. Physical properties and alkalinity results by site,Voyageurs National Park, Minnesota, 2001—Continued. 
Date 

Air 

Pressure 

(mm Hg)

Water 

Temperature 

(°C)

Secchi disk 

transparency (m)

Specific 

conductance, 

field (μS/cm)

Specific conductance, 

laboratory 

(μS/cm) Field pH

Laboratory 

pH

Dissolved 

oxygen 

(mg/L)

Total 

alkalinity 

as CaC03

(mg/L)

Bicarbonate alkalinity as HCO3 

(mg/L)

Carbonate 

alkalinity 

as CO3 

(mg/L)

Kabetogama Lake at Cemetary Island near Ray, Site 43—Continued

5/14/02 -- 8.0 1.8 102 -- 8.0 -- 13.3 -- -- --

5/30/02 -- 14.6 2.2 99 -- 7.5 -- 5.1 -- -- --

6/12/02 -- 15.8 2.5 100 -- 7.4 -- -- -- -- --

6/26/02 -- 19.9 2.8 76 -- 7.5 -- 9.0 -- -- --

7/9/02 -- 22.8 2.0 94 -- 8.5 -- 10.0 -- -- --

7/23/02 -- 22.1 1.5 94 -- 7.7 -- 7.4 -- -- --

8/6/02 -- 21.3 1.3 93 -- 8.9 -- 11.0 -- -- --

8/21/02 731 19.4 1.8 86 -- 8.4 -- 11.1 -- -- --

9/5/02 -- 20.3 1.8 88 -- 8.0 -- 7.7 -- -- --

9/17/02 -- 19.6 2.5 87 -- 7.5 -- 7.4 -- -- --

9/30/02 -- 14.0 2.2 75 -- 7.4 -- 8.9 -- -- --

10/16/02 -- 8.0 4.0 64 -- 7.6 -- 10.0 -- -- --

5/14/03 -- 12.7 1.7 106 -- 8.0 -- 10.6 34 42 0

5/29/03 -- 15.6 1.7 92 -- 7.4 -- 10.2 42 51 0

6/10/03 -- 17.6 2.6 93 -- 7.4 -- 8.9 -- -- --

6/24/03 -- 21.1 3.8 95 -- 7.9 -- 8.6 -- -- --

7/8/03 -- 19.8 3.0 100 -- 7.8 -- 8.3 -- -- --

7/22/03 -- 21.4 2.3 101 -- 8.1 -- 8.7 -- -- --

8/5/03 -- 22.9 2.8 101 -- 8.8 -- 8.7 -- -- --

8/19/03 -- 25.0 1.5 103 -- 9.1 -- 8.2 -- -- --

9/3/03 -- 19.6 1.5 101 -- 8.0 -- 8.3 -- -- --

9/17/03 -- 19.0 2.4 102 -- 6.8 -- 5.9 41 50 0

9/29/03 -- 12.6 3.1 99 -- 7.1 -- 8.0 38 47 0

Kabetogama Lake near Grave Island near Ray, Site 45 

5/17/01 -- 11.2 2.0 97 101 7.8 7.6 11.4 41 50 0

5/31/01 -- 14.1 2.5 98 -- 7.4 -- 6.8 -- -- --

6/12/01 -- 16.9 2.8 94 -- 7.3 -- -- 37 45 0

6/26/01 -- 21.0 2.9 96 -- 7.8 -- 9.0 50 60 0

7/10/01 -- 20.8 2.1 95 -- 7.8 -- 9.0 36 44 0

7/24/01 -- 21.9 2.9 95 -- 7.4 -- 10.3 38 47 0

8/7/01 -- 25.2 1.1 94 -- 9.1 -- 9.6 50 60 --

8/22/01 731 22.3 1.3 100 98 8.9 8.6 10.0 44 53 4

9/5/01 -- 21.0 1.4 98 -- 7.6 -- 5.8 31 38 0

9/18/01 -- 18.4 1.6 98 -- 7.8 -- 8.2 41 50 0

10/2/01 -- 16.0 2.1 101 -- 7.7 -- 8.0 56 68 0

10/16/01 -- 11.3 3.0 101 -- 7.6 -- 8.5 40 49 0

5/14/02 -- 6.8 2.7 109 -- 7.5 -- 12.8 -- -- --

5/30/02 -- 15.3 2.3 91 -- 8.0 -- 4.9 48 58 0

6/12/02 -- 14.7 2.5 96 -- 7.4 -- -- -- -- --

6/26/02 -- 18.3 2.5 72 -- 7.7 -- 8.3 -- -- --

7/9/02 -- 23.4 2.0 94 -- 8.5 -- 9.9 -- -- --

7/23/02 -- 22.6 2.0 95 -- 7.9 -- 8.7 -- -- --

8/6/02 -- 21.5 1.5 92 -- 8.2 -- 9.4 -- -- --

8/21/02 730 19.5 1.7 86 -- 8.1 -- 10.0 -- -- --

9/5/02 -- 20.1 1.5 88 -- 7.8 -- 7.9 -- -- --

9/17/02 -- 19.7 2.3 87 -- 7.6 -- 8.4 -- -- --

Table 8. Physical properties and alkalinity results by site,Voyageurs National Park, Minnesota, 2001—Continued. 

Appendix 25
26 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date 

Air 

Pressure 

(mm Hg)

Water 

Temperature 

(°C)

Secchi disk 

transparency (m)

Specific 

conductance, 

field (μS/cm)

Specific conductance, 

laboratory 

(μS/cm) Field pH

Laboratory 

pH

Dissolved 

oxygen 

(mg/L)

Total 

alkalinity 

as CaC03

(mg/L)

Bicarbonate alkalinity as HCO3 

(mg/L)

Carbonate 

alkalinity 

as CO3 

(mg/L)

Kabetogama Lake near Grave Island near Ray, Site 45 —Continued

9/30/02 -- 15.1 2.0 76 -- 7.6 -- 9.1 -- -- --

10/16/02 -- 9.6 3.3 65 -- 7.6 -- 10.2 -- -- --

5/14/03 -- 11.8 1.7 108 -- 7.8 -- 11.6 35 43 0

5/29/03 -- 13.9 1.7 92 -- 7.5 -- 11.6 41 50 0

6/10/03 -- 17.0 2.8 92 -- -- -- 9.6 -- -- --

6/24/03 -- 21.5 -- 93 -- 8.2 -- 9.0 -- -- --

7/8/03 -- 19.5 2.7 97 -- 7.6 -- 8.0 -- -- --

7/22/03 -- 21.6 2.6 98 -- 8.4 -- 8.5 -- -- --

8/5/03 -- 23.4 2.9 98 -- 9.0 -- 9.2 -- -- --

8/19/03 -- 25.6 1.8 101 -- 9.2 -- 8.8 -- -- --

9/3/03 -- 20.0 1.8 100 -- 7.7 -- 7.1 -- -- --

9/17/03 -- 19.2 2.9 100 -- 7.4 -- 7.1 40 49 0

9/29/03 -- 13.5 3.0 99 -- 7.5 -- 8.8 39 48 0

Rainy Lake at Black Bay Narrows near International Falls, Site 1

5/15/01 -- 10.4 0.9 -- 88 7.3 7.6 11.3 35 43 0

5/29/01 -- 14.6 0.9 99 -- 7.7 -- 9.9 -- -- --

6/11/01 -- 20.4 1.3 96 -- 7.5 -- 8.5 40 49 0

6/25/01 -- 22.0 1.1 98 -- 7.5 -- 6.0 35 43 0

7/9/01 -- 24.0 1.0 98 -- 8.2 -- -- 39 47 0

7/23/01 -- 26.4 1.3 99 -- 7.7 -- 12.4 36 44 0

8/6/01 -- 29.5 0.8 99 -- 8.0 -- 7.3 43 52 0

8/20/01 735 21.4 0.9 103 105 7.8 7.5 7.9 47 57 0

9/4/01 -- 19.5 0.8 101 -- 7.6 -- 9.2 43 52 0

9/17/01 -- 16.8 1.0 76 -- 7.5 -- 8.2 29 36 0

10/1/01 -- 14.1 0.8 97 -- 7.5 -- 8.6 54 66 0

10/16/01 -- 8.0 1.0 91 -- 7.8 -- 13.3 38 47 0

5/13/02 -- 11.3 0.9 103 -- 7.8 -- 11.9 -- -- --

5/28/02 -- 14.5 1.2 108 -- 7.7 -- 6.6 -- -- --

6/11/02 -- 13.9 1.0 66 -- 7.5 -- -- -- -- --

6/24/02 -- 20.5 1.0 81 -- 8.2 -- 8.3 -- -- --

7/8/02 -- 22.5 1.5 107 -- 7.5 -- 6.9 -- -- --

7/22/02 -- 24.3 1.0 103 -- 7.5 -- 10.3 -- -- --

8/5/02 -- 20.7 0.8 93 -- 8.2 -- 8.9 -- -- --

8/20/02 -- 17.6 0.7 96 -- 8.1 -- 8.6 -- -- --

9/4/02 -- 19.6 0.5 79 -- 7.9 -- 8.4 -- -- --

9/16/02 -- 17.5 1.0 62 -- 7.9 -- 8.9 -- -- --

10/2/02 -- 11.4 0.8 66 -- 7.3 -- 6.1 -- -- --

10/15/02 -- 5.5 0.8 58 -- 7.6 -- 12.0 -- -- --

5/13/03 -- 13.8 0.7 86 -- 7.8 -- 10.7 26 32 0

5/28/03 -- 14.5 0.9 55 -- 7.3 -- 10.3 22 27 0

6/9/03 -- 18.0 0.9 79 -- -- -- 7.3 -- -- --

6/23/03 -- 19.5 0.9 61 -- 7.6 -- 9.2 -- -- --

7/7/03 -- 21.3 0.5 103 -- 7.9 -- 8.4 -- -- --

7/21/03 -- 22.7 0.9 79 -- 7.8 -- 7.7 -- -- --

8/4/03 -- 22.6 0.9 78 -- 8.3 -- 7.7 -- -- --

8/18/03 -- 24.3 0.7 73 -- 8.5 -- 8.5 -- -- --

Table 8. Physical properties and alkalinity results by site,Voyageurs National Park, Minnesota, 2001—Continued. 
Date 

Air 

Pressure 

(mm Hg)

Water 

Temperature 

(°C)

Secchi disk 

transparency (m)

Specific 

conductance, 

field (μS/cm)

Specific conductance, 

laboratory 

(μS/cm) Field pH

Laboratory 

pH

Dissolved 

oxygen 

(mg/L)

Total 

alkalinity 

as CaC03

(mg/L)

Bicarbonate alkalinity as HCO3 

(mg/L)

Carbonate 

alkalinity 

as CO3 

(mg/L)

Rainy Lake at Black Bay Narrows near International Falls, Site 1—Continued

9/2/03 -- 18.0 0.3 97 -- 7.1 -- 7.3 -- -- --

9/15/03 -- 17.5 0.8 61 -- 7.1 -- 7.4 20 24 0

9/28/03 -- 8.8 0.3 70 -- 7.4 -- 9.9 24 29 0

Rainy Lake at Black Bay near International Falls, Site 16 

5/15/01 -- 12.7 0.7 93 91 7.7 7.5 11.0 37 45 0

5/29/01 -- 13.0 0.5 89 -- 8.0 -- 10.2 -- -- --

6/11/01 -- 19.1 1.0 93 -- 7.4 -- 9.1 -- -- --

6/25/01 -- 22.0 1.5 95 -- 7.5 -- 6.8 -- -- --

7/9/01 -- 22.9 1.3 94 -- 7.9 -- 8.6 -- -- --

7/23/01 -- 25.9 1.3 100 -- 7.3 -- 11.1 -- -- --

8/6/01 -- 26.9 0.7 89 -- 8.8 -- 8.8 -- -- --

8/20/01 736 20.8 1.2 98 95 7.7 7.7 7.2 42 51 0

9/4/01 -- 20.0 0.9 96 -- 7.5 -- 7.3 -- -- --

9/17/01 -- 17.0 1.3 100 -- 7.4 -- 6.5 -- -- --

10/1/01 -- 15.0 1.2 100 -- 7.4 -- 7.3 -- -- --

10/16/01 -- 7.7 0.8 92 -- 8.5 -- 13.5 -- -- --

5/13/02 -- 10.3 0.6 104 -- 7.5 -- 11.6 -- -- --

5/28/02 -- 13.8 1.3 101 -- 7.7 -- 6.2 -- -- --

6/11/02 -- 15.4 1.0 98 -- 7.5 -- -- -- -- --

6/24/02 -- 19.7 1.5 42 -- 8.2 -- 7.7 -- -- --

7/8/02 -- 21.8 1.8 92 -- 7.9 -- 8.9 -- -- --

7/22/02 -- 24.0 0.5 100 -- 7.7 -- 11.2 -- -- --

8/5/02 -- 20.9 1.0 93 -- 8.2 -- 9.2 -- -- --

8/20/02 731 18.7 0.6 95 -- 8.2 -- 8.9 -- -- --

9/4/02 -- 19.4 0.8 89 -- 7.9 -- 7.8 -- -- --

9/16/02 -- 17.2 1.0 84 -- 7.9 -- 8.0 -- -- --

10/2/02 -- 11.9 0.8 72 -- 7.3 -- 3.9 -- -- --

10/15/02 -- 6.1 0.5 61 -- 7.5 -- 11.0 -- -- --

5/13/03 -- 13.9 0.6 100 -- 7.7 -- 10.1 35 43 0

5/28/03 -- 18.0 0.3 85 -- 7.4 -- 8.7 39 48 0

6/9/03 -- 17.4 0.7 86 -- -- -- 4.5 -- -- --

Rainy Lake at Black Bay (West) near International Falls, Site 44

5/15/01 -- 15.4 0.8 99 103 7.4 7.5 8.5 43 52 0

5/29/01 -- 14.8 0.7 115 -- 7.7 -- 8.8 -- -- --

6/11/01 -- 19.7 1.0 103 -- 6.9 -- 6.7 40 49 0

6/25/01 -- 22.2 1.2 104 -- 7.5 -- 7.0 38 47 0

7/9/01 -- 22.7 0.8 102 -- 7.7 -- 6.4 44 54 0

7/23/01 -- 25.2 1.2 105 -- 7.6 -- 10.3 49 60 0

8/6/01 -- 25.9 0.7 96 -- 7.3 -- 4.7 39 48 0

8/20/01 735 22.2 0.6 106 107 7.9 8.1 8.3 49 59 0

9/4/01 -- 19.5 0.5 113 -- 7.6 -- 8.3 47 57 0

9/17/01 -- 15.9 0.6 104 -- 7.5 -- 7.4 45 54 0

10/1/01 -- 14.0 0.8 103 -- 7.5 -- 8.3 44 53 0

10/16/01 -- 7.7 0.8 97 -- 7.9 -- 13.2 59 72 0

5/13/02 -- 11.7 0.7 129 -- 7.3 -- 10.7 -- -- --

5/28/02 -- 15.6 2.2 113 -- 7.6 -- 5.5 -- -- --

6/11/02 -- 15.8 0.5 107 -- 7.9 -- -- -- -- --

Table 8. Physical properties and alkalinity results by site,Voyageurs National Park, Minnesota, 2001—Continued. 

Appendix 27
28 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date 

Air 

Pressure 

(mm Hg)

Water 

Temperature 

(°C)

Secchi disk 

transparency (m)

Specific 

conductance, 

field (μS/cm)

Specific conductance, 

laboratory 

(μS/cm) Field pH

Laboratory 

pH

Dissolved 

oxygen 

(mg/L)

Total 

alkalinity 

as CaC03

(mg/L)

Bicarbonate alkalinity as HCO3 

(mg/L)

Carbonate 

alkalinity 

as CO3 

(mg/L)

Rainy Lake at Black Bay (West) near International Falls, Site 44—Continued

6/24/02 -- 20.1 0.8 109 -- 7.8 -- 10.5 -- -- --

7/8/02 -- 21.6 0.5 96 -- 7.4 -- 6.5 -- -- --

7/22/02 -- 23.6 0.8 102 -- 7.2 -- 9.3 -- -- --

8/5/02 -- 20.7 0.8 93 -- 8.4 -- 9.5 -- -- --

8/20/02 734 17.9 0.6 96 -- 8.2 -- 8.7 -- -- --

9/4/02 -- 19.3 0.8 88 -- 7.8 -- 8.1 -- -- --

9/16/02 -- 17.4 0.5 84 -- 8.1 -- 9.2 -- -- --

10/2/02 -- 10.9 0.8 72 -- 7.3 -- 4.8 -- -- --

10/15/02 -- 5.5 0.8 61 -- 7.0 -- 11.6 -- -- --

5/13/03 -- 13.0 0.6 98 -- 7.7 -- 10.3 33 40 0

5/28/03 732 18.1 -- 85 -- 7.2 -- 8.4 38 46 0

6/9/03 -- 19.6 0.4 91 -- -- -- 7.5 -- -- --

6/23/03 -- 22.6 0.5 98 -- 7.3 -- 7.3 -- -- --

7/7/03 -- 20.6 0.1 157 -- 7.5 -- 7.9 -- -- --

7/21/03 -- 22.0 0.3 114 -- 7.2 -- 6.9 -- -- --

8/4/03 -- 23.8 0.3 108 -- 8.8 -- 9.2 -- -- --

8/18/03 -- 27.3 0.2 115 -- 9.1 -- 9.3 -- -- --

9/2/03 -- 18.9 0.2 109 -- 6.4 -- 6.6 -- -- --

9/15/03 -- 17.1 0.2 103 -- 6.5 -- 7.0 38 46 0

9/28/03 -- 8.0 0.1 94 -- 6.7 -- 9.6 35 43 0

Table 8. Physical properties and alkalinity results by site,Voyageurs National Park, Minnesota, 2001—Continued. 
Date 

Dissolved 

solids

Dissolved 

calcium 

Dissolved 

magnesium 

Dissolved 

potassium

Dissolved 

sodium

Dissolved 

chloride

Dissolved 

sulfate

Dissolved 

manganese

Sand Point Lake below Harrison Narrows near Crane Lake, Site 7

5/16/01 54 5.8 2.3 1.0 1.9 2.1 4.1 6.2

8/21/01 61 6.3 2.5 1.2 1.8 2.5 3.4 5.2

Namakan Lake near Ray, Site 14 

5/16/01 44 4.9 1.8 0.6 1.3 1.1 2.8 E1.9

8/21/01 44 4.9 1.8 0.6 1.4 1.7 3.1 <3.0

Rainy Lake at Brule Narrows near International Falls, Site 5

5/15/01 49 5.2 1.8 0.6 1.3 1.0 2.8 <3.0

8/20/01 42 5.0 1.9 0.7 1.3 1.1 3.4 <3.0

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11

8/21/01 76 11.7 4.5 1.0 1.4 1.1 2.1 <3.0

Kabetogama Lake at Cemetary Island near Ray, Site 43 

5/17/01 59 10.6 4.1 0.8 1.5 1.2 2.5 <3.0

8/22/01 63 11.3 4.4 0.9 1.5 1.3 2.3 <3.0

Kabetogama Lake near Grave Island near Ray, Site 45 

5/17/01 65 12.0 4.6 1.0 1.5 1.3 2.5 <3.0

8/22/01 68 11.7 4.5 1.0 1.5 1.3 2.2 <3.0

Rainy Lake at Black Bay Narrows near International Falls, Site 1

5/15/01 75 10.6 4.4 1.0 1.3 1.2 2.2 E1.9

8/20/01 97 12.7 5.2 1.1 1.3 1.0 1.8 7.9

Rainy Lake at Black Bay near International Falls, Site 16 

5/15/01 57 10.4 4.0 0.8 1.4 1.2 2.5 <3.0

8/20/01 66 11.5 4.5 1.0 1.5 1.2 2.8 <3.0

Rainy Lake at Black Bay (West) near International Falls, Site 44

5/15/01 94 12.9 5.5 1.1 1.4 1.2 2.0 E2.5

8/20/01 104 13.6 5.6 1.2 1.4 1.1 2.2 7.7

Table 9. Dissolved solids and major ion analytical results by site, Voyageurs National Park, Minnesota, 2001

(all units in milligrams per liter)

Appendix 29
30 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date 

Dissolved 

nitrate 

nitrogen

Dissolved 

nitrite 

nitrogen

Dissolved 

nitrite plus 

nitrate 

nitrogen

Dissolved 

ammonia 

nitrogen

Dissolved 

ammonia 

plus organic 

nitrogen

Total 

ammonia 

plus organic 

nitrogen

Total

 phosphorus

Dissolved 

phosphorus

Dissolved 

orthophosphorus

Sand Point Lake below Harrison Narrows near Crane Lake, Site 7

5/16/01 0.0 0.0 0.0 0.0 0.4 0.6 0.0 0.0 <0.007

8/21/01 0.0 0.0 0.0 0.0 0.6 0.6 0.0 0.0 <0.007

5/14/02 0.1 0.0 0.1 <0.015 0.4 0.5 0.0 0.0 <0.007

8/21/02 0.0 0.0 0.0 E0.011 0.4 0.5 0.0 0.0 <0.007

5/29/03 -- E0.002 <0.022 E0.010 0.4 0.6 0.0 0.0 <0.007

Namakan Lake near Ray, Site 14 

5/16/01 0.0 0.0 0.0 0.0 0.3 0.5 0.0 E0.005 <0.007

8/21/01 0.0 0.0 0.0 0.0 0.3 0.4 0.0 E0.003 <0.007

5/14/02 E0.09 E0.002 0.0 E0.014 0.3 0.4 0.0 0.0 <0.007

8/21/02 E0.053 E0.002 0.0 E0.009 0.3 0.5 0.0 0.0 <0.007

5/29/03 0.0 0.0 0.0 <0.015 0.3 0.4 0.0 E0.004 <0.007

Rainy Lake at Brule Narrows near International Falls, Site 5

5/15/01 0.0 0.0 0.0 <0.002 0.3 0.4 0.0 0.0 <0.007

8/20/01 0.0 0.0 0.0 0.0 0.3 0.4 0.0 E0.003 <0.007

5/13/02 E0.085 E0.002 0.0 <0.015 0.3 0.4 0.0 0.0 <0.007

8/20/02 E0.092 E0.002 0.0 <0.015 0.3 0.4 0.0 0.0 <0.007

5/28/03 E0.038 E0.002 0.0 <0.015 0.3 0.4 0.0 0.0 <0.007

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11

5/30/01 -- -- -- -- -- -- 0.0 -- --

6/12/01 -- -- -- -- -- -- 0.0 -- --

6/25/01 -- -- -- -- -- -- 0.0 -- --

7/10/01 -- -- -- -- -- -- 0.0 -- --

7/24/01 -- -- -- -- -- -- 0.0 -- --

8/7/01 -- -- -- -- -- -- 0.0 -- --

8/21/01 -- 0.0 <0.005 0.0 0.5 0.7 0.0 0.0 <0.007

9/5/01 -- -- -- -- -- -- 0.0 -- --

9/18/01 -- -- -- -- -- -- 0.0 -- --

10/2/01 -- -- -- -- -- -- 0.0 -- --

10/17/01 -- -- -- -- -- -- 0.0 -- --

5/14/02 E0.033 E0.002 0.0 <0.015 0.3 0.5 0.0 0.0 <0.007

5/30/02 -- -- -- -- -- -- 0.0 -- --

6/12/02 -- -- -- -- -- -- 0.0 -- --

6/26/02 -- -- -- -- -- -- 0.0 -- --

7/9/02 -- -- -- -- -- -- 0.0 -- --

7/23/02 -- -- -- -- -- -- 0.0 -- --

8/6/02 -- -- -- -- -- -- 0.0 -- --

8/21/02 -- <0.002 <0.013 <0.015 0.4 0.8 0.0 0.0 0.0

9/5/02 -- -- -- -- -- -- 0.0 -- --

Table 10. Nutrient analytical results by site, Voyageurs National Park, Minnesota, 2001-03.

[all units in milligrams per liter; --, not determined; <, less than; E, estimated]
Date 

Dissolved 

nitrate 

nitrogen

Dissolved 

nitrite 

nitrogen

Dissolved 

nitrite plus 

nitrate 

nitrogen

Dissolved 

ammonia 

nitrogen

Dissolved 

ammonia 

plus organic 

nitrogen

Total 

ammonia 

plus organic 

nitrogen

Total

 phosphorus

Dissolved 

phosphorus

Dissolved 

orthophosphorus

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11—Continued

9/17/02 -- -- -- -- -- -- 0.0 -- --

9/30/02 -- -- -- -- -- -- 0.0 -- --

10/16/02 -- -- -- -- -- -- 0.0 -- --

5/14/03 -- -- -- -- -- -- 0.0 -- --

5/29/03 -- <0.002 <0.022 <0.015 0.3 0.6 -- 0.0 <0.007

6/10/03 -- -- -- -- -- -- 0.0 -- --

6/24/03 -- -- -- -- -- -- 0.0 -- --

7/8/03 -- -- -- -- -- -- 0.0 -- --

7/22/03 -- -- -- -- -- -- 0.0 -- --

8/5/03 -- -- -- -- -- -- 0.0 -- --

8/19/03 -- -- -- -- -- -- 0.0 -- --

9/3/03 -- -- -- -- -- -- 0.0 -- --

9/17/03 -- -- -- -- -- -- 0.0 -- --

Kabetogama Lake at Cemetary Island near Ray, Site 43 

5/17/01 -- <0.001 <0.005 0.0 0.3 0.5 0.0 0.0 <0.007

5/31/01 -- -- -- -- -- -- 0.0 -- --

6/12/01 -- -- -- -- -- -- 0.0 -- --

6/26/01 -- -- -- -- -- -- 0.0 -- --

7/10/01 -- -- -- -- -- -- 0.0 -- --

7/24/01 -- -- -- -- -- -- 0.0 -- --

8/7/01 -- -- -- -- -- -- 0.0 -- --

8/22/01 0.0 0.0 0.0 0.0 0.4 0.9 0.0 0.0 <0.007

9/5/01 -- -- -- -- -- -- 0.0 -- --

9/18/01 -- -- -- -- -- -- 0.0 -- --

10/2/01 -- -- -- -- -- -- 0.0 -- --

10/17/01 -- -- -- -- -- -- 0.0 -- --

5/14/02 -- <0.002 <0.013 <0.015 0.3 0.5 0.0 0.0 <0.007

5/30/02 -- -- -- -- -- -- 0.0 -- --

6/12/02 -- -- -- -- -- -- 0.0 -- --

6/26/02 -- -- -- -- -- -- 0.0 -- --

7/9/02 -- -- -- -- -- -- 0.0 -- --

7/23/02 -- -- -- -- -- -- 0.0 -- --

8/6/02 -- -- -- -- -- -- 0.0 -- --

8/21/02 -- <0.002 <0.013 0.0 0.4 0.7 0.0 0.0 0.0

9/5/02 -- -- -- -- -- -- 0.0 -- --

9/17/02 -- -- -- -- -- -- 0.0 -- --

9/30/02 -- -- -- -- -- -- 0.0 -- --

10/16/02 -- -- -- -- -- -- 0.0 -- --

5/14/03 -- -- -- -- -- -- 0.0 -- --

Table 10. Nutrient analytical results by site, Voyageurs National Park, Minnesota, 2001-03—Contintued.

Appendix 31
32 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date 

Dissolved 

nitrate 

nitrogen

Dissolved 

nitrite 

nitrogen

Dissolved 

nitrite plus 

nitrate 

nitrogen

Dissolved 

ammonia 

nitrogen

Dissolved 

ammonia 

plus organic 

nitrogen

Total 

ammonia 

plus organic 

nitrogen

Total

 phosphorus

Dissolved 

phosphorus

Dissolved 

orthophosphorus

Kabetogama Lake at Cemetary Island near Ray, Site 43 —Continued

5/29/03 -- <0.002 <0.022 <0.015 0.3 0.5 -- 0.0 <0.007

6/10/03 -- -- -- -- -- -- 0.0 -- --

6/24/03 -- -- -- -- -- -- 0.0 -- --

7/8/03 -- -- -- -- -- -- 0.0 -- --

7/22/03 -- -- -- -- -- -- 0.0 -- --

8/5/03 -- -- -- -- -- -- 0.0 -- --

8/19/03 -- -- -- -- -- -- 0.0 -- --

9/3/03 -- -- -- -- -- -- 0.0 -- --

9/17/03 -- -- -- -- -- -- 0.1 -- --

Kabetogama Lake near Grave Island near Ray, Site 45 

5/17/01 -- 0.0 <0.005 0.0 0.3 0.5 0.0 0.0 <0.007

5/31/01 -- -- -- -- -- -- 0.0 -- --

6/12/01 -- -- -- -- -- -- 0.0 -- --

6/26/01 -- -- -- -- -- -- 0.0 -- --

7/10/01 -- -- -- -- -- -- 0.0 -- --

7/24/01 -- -- -- -- -- -- 0.0 -- --

8/7/01 -- -- -- -- -- -- 0.0 -- --

8/22/01 -- <0.001 0.0 0.0 0.4 1.1 0.0 0.0 <0.007

9/5/01 -- -- -- -- -- -- 0.0 -- --

9/18/01 -- -- -- -- -- -- 0.0 -- --

10/2/01 -- -- -- -- -- -- 0.0 -- --

10/17/01 -- -- -- -- -- -- 0.0 -- --

5/14/02 -- <0.002 0.0 <0.015 0.4 0.5 0.0 0.0 <0.007

6/12/02 -- -- -- -- -- -- 0.0 -- --

6/26/02 -- -- -- -- -- -- 0.0 -- --

7/9/02 -- -- -- -- -- -- 0.0 -- --

7/23/02 -- -- -- -- -- -- 0.0 -- --

8/6/02 -- -- -- -- -- -- 0.1 -- --

8/21/02 -- <0.002 <0.013 0.0 0.4 0.8 0.0 0.0 0.0

9/5/02 -- -- -- -- -- -- 0.0 -- --

9/17/02 -- -- -- -- -- -- 0.0 -- --

9/30/02 -- -- -- -- -- -- 0.1 -- --

10/16/02 -- -- -- -- -- -- 0.0 -- --

5/14/03 -- -- -- -- -- -- 0.0 -- --

5/29/03 -- <0.002 <0.022 <0.015 0.3 0.6 -- E0.004 <0.007

6/10/03 -- -- -- -- -- -- 0.0 -- --

6/24/03 -- -- -- -- -- -- 0.0 -- --

7/8/03 -- -- -- -- -- -- 0.0 -- --

7/22/03 -- -- -- -- -- -- 0.0 -- --

Table 10. Nutrient analytical results by site, Voyageurs National Park, Minnesota, 2001-03—Contintued.
Date 

Dissolved 

nitrate 

nitrogen

Dissolved 

nitrite 

nitrogen

Dissolved 

nitrite plus 

nitrate 

nitrogen

Dissolved 

ammonia 

nitrogen

Dissolved 

ammonia 

plus organic 

nitrogen

Total 

ammonia 

plus organic 

nitrogen

Total

 phosphorus

Dissolved 

phosphorus

Dissolved 

orthophosphorus

Kabetogama Lake near Grave Island near Ray, Site 45— Continued

8/5/03 -- -- -- -- -- -- 0.0 -- --

8/19/03 -- -- -- -- -- -- 0.0 -- --

9/3/03 -- -- -- -- -- -- 0.0 -- --

9/17/03 -- -- -- -- -- -- 0.0 -- --

Rainy Lake at Black Bay Narrows near International Falls, Site 1

5/15/01 -- 0.0 <0.005 0.0 0.4 0.7 0.0 0.0 <0.007

5/29/01 -- -- -- -- -- -- 0.0 -- --

6/11/01 -- -- -- -- -- -- 0.0 -- --

6/25/01 -- -- -- -- -- -- 0.0 -- --

7/9/01 -- -- -- -- -- -- 0.0 -- --

7/23/01 -- -- -- -- -- -- 0.0 -- --

8/6/01 -- -- -- -- -- -- 0.0 -- --

8/20/01 -- 0.0 <0.005 0.0 0.7 0.9 0.0 0.0 E0.005

9/4/01 -- -- -- -- -- -- 0.0 -- --

9/17/01 -- -- -- -- -- -- 0.0 -- --

10/1/01 -- -- -- -- -- -- 0.0 -- --

10/16/01 -- -- -- -- -- -- 0.0 -- --

5/13/02 -- E0.002 <0.013 <0.015 0.4 0.7 0.0 0.0 <0.007

5/28/02 -- -- -- -- -- -- 0.0 -- --

6/11/02 -- -- -- -- -- -- 0.0 -- --

6/24/02 -- -- -- -- -- -- 0.0 -- --

7/8/02 -- -- -- -- -- -- 0.0 -- --

7/22/02 -- -- -- -- -- -- 0.0 -- --

8/5/02 -- -- -- -- -- -- 0.0 -- --

8/20/02 0.0 0.0 0.0 0.0 0.6 0.9 0.0 0.0 0.0

9/4/02 -- -- -- -- -- -- 0.0 -- --

9/16/02 -- -- -- -- -- -- 0.0 -- --

10/2/02 -- -- -- -- -- -- 0.0 -- --

10/15/02 -- -- -- -- -- -- 0.0 -- --

5/13/03 -- -- -- -- -- -- 0.0 -- --

5/28/03 E0.023 E0.002 0.0 <0.015 0.3 0.5 0.0 0.0 <.007

6/9/03 -- -- -- -- -- -- 0.0 -- --

6/23/03 -- -- -- -- -- -- 0.0 -- --

7/7/03 -- -- -- -- -- -- 0.0 -- --

7/21/03 -- -- -- -- -- -- 0.0 -- --

8/4/03 -- -- -- -- -- -- 0.0 -- --

8/18/03 -- -- -- -- -- -- 0.0 -- --

9/2/03 -- -- -- -- -- -- 0.0 -- --

9/15/03 -- -- -- -- -- -- 0.0 -- --

Table 10. Nutrient analytical results by site, Voyageurs National Park, Minnesota, 2001-03—Contintued.

Appendix 33
34 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date 

Dissolved 

nitrate 

nitrogen

Dissolved 

nitrite 

nitrogen

Dissolved 

nitrite plus 

nitrate 

nitrogen

Dissolved 

ammonia 

nitrogen

Dissolved 

ammonia 

plus organic 

nitrogen

Total 

ammonia 

plus organic 

nitrogen

Total

 phosphorus

Dissolved 

phosphorus

Dissolved 

orthophosphorus

Rainy Lake at Black Bay near International Falls, Site 16 

5/15/01 -- 0.0 <0.005 0.0 0.3 0.5 0.0 E0.006 <0.007

5/29/01 -- -- -- -- -- -- 0.0 -- --

6/11/01 -- -- -- -- -- -- 0.0 -- --

6/25/01 -- -- -- -- -- -- 0.0 -- --

7/9/01 -- -- -- -- -- -- 0.0 -- --

7/23/01 -- -- -- -- -- -- 0.0 -- --

8/6/01 -- -- -- -- -- -- 0.0 -- --

8/20/01 -- <0.001 0.0 0.0 0.3 0.6 0.0 0.0 <0.007

9/4/01 -- -- -- -- -- -- 0.0 -- --

9/17/01 -- -- --’ -- -- -- 0.0 -- --

10/1/01 -- -- -- -- -- -- 0.0 -- --

10/16/01 -- -- -- -- -- -- 0.0 -- --

5/13/02 -- E0.002 <0.013 <0.015 0.4 0.7 0.0 0.0 <0.007

5/28/02 -- -- -- -- -- -- 0.0 -- --

6/11/02 -- -- -- -- -- -- 0.0 -- --

6/24/02 -- -- -- -- -- -- 0.0 -- --

7/8/02 -- -- -- -- -- -- 0.0 -- --

7/22/02 -- -- -- -- -- -- 0.1 -- --

8/5/02 -- -- -- -- -- -- 0.1 -- --

8/20/02 0.0 0.0 0.0 E0.009 0.5 0.8 0.1 0.0 0.0

9/4/02 -- -- -- -- -- -- 0.1 -- --

9/16/02 -- -- -- -- -- -- 0.1 -- --

10/2/02 -- -- -- -- -- -- 0.1 -- --

10/15/02 -- -- -- -- -- -- 0.1 -- --

5/13/03 -- -- -- -- -- -- 0.1 -- --

5/28/03 E0.012 E0.002 E0.014 E0.008 0.4 1.1 0.1 0.0 <0.007

6/9/03 -- -- -- -- -- -- 0.1 -- --

Rainy Lake at Black Bay (West) near International Falls, Site 44

5/15/01 0.0 0.0 0.0 0.0 0.6 0.8 0.0 0.0 <0.007

5/29/01 -- -- -- -- -- -- 0.0 -- --

6/11/01 -- -- -- -- -- -- 0.0 -- --

6/25/01 -- -- -- -- -- -- 0.0 -- --

7/9/01 -- -- -- -- -- -- 0.0 -- --

7/23/01 -- -- -- -- -- -- 0.0 -- --

8/6/01 -- -- -- -- -- -- 0.1 -- --

8/20/01 0.0 0.0 0.0 0.0 0.7 1.1 0.1 0.0 <0.007

9/4/01 -- -- -- -- -- -- 0.1 -- --

9/17/01 -- -- -- -- -- -- 0.1 -- --

10/1/01 -- -- -- -- -- -- 0.0 -- --

Table 10. Nutrient analytical results by site, Voyageurs National Park, Minnesota, 2001-03—Contintued.
Date 

Dissolved 

nitrate 

nitrogen

Dissolved 

nitrite 

nitrogen

Dissolved 

nitrite plus 

nitrate 

nitrogen

Dissolved 

ammonia 

nitrogen

Dissolved 

ammonia 

plus organic 

nitrogen

Total 

ammonia 

plus organic 

nitrogen

Total

 phosphorus

Dissolved 

phosphorus

Dissolved 

orthophosphorus

Rainy Lake at Black Bay (West) near International Falls, Site 44—Continued

10/16/01 -- -- -- -- -- -- 0.0 -- --

5/13/02 -- 0.0 <0.013 <0.015 0.6 0.9 0.0 0.0 <0.007

6/11/02 -- -- -- -- -- -- 0.0 -- --

6/24/02 -- -- -- -- -- -- 0.0 -- --

7/8/02 -- -- -- -- -- -- 0.1 -- --

7/22/02 -- -- -- -- -- -- 0.1 -- --

8/5/02 -- -- -- -- -- -- 0.1 -- --

8/20/02 0.0 0.0 0.0 E0.013 0.5 0.7 0.1 0.0 0.0

9/4/02 -- -- -- -- -- -- 0.1 -- --

9/16/02 -- -- -- -- -- -- 0.1 -- --

10/2/02 -- -- -- -- -- -- 0.0 -- --

10/15/02 -- -- -- -- -- -- 0.1 -- --

5/13/03 -- -- -- -- -- -- 0.1 -- --

5/28/03 E0.011 E0.002 E0.013 0.0 0.4 0.7 0.0 0.0 <0.007

6/9/03 -- -- -- -- -- -- 0.1 -- --

6/23/03 -- -- -- -- -- -- 0.1 -- --

7/7/03 -- -- -- -- -- -- 0.2 -- --

7/21/03 -- -- -- -- -- -- 0.1 -- --

8/4/03 -- -- -- -- -- -- 0.1 -- --

8/18/03 -- -- -- -- -- -- 0.1 -- --

9/2/03 -- -- -- -- -- -- 0.1 -- --

9/15/03 -- -- -- -- -- -- 0.1 -- --

Table 10. Nutrient analytical results by site, Voyageurs National Park, Minnesota, 2001-03—Contintued.

Appendix 35
36 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date Chlorophyll-a Chlorophyll-b

Sand Point Lake below Harrison Narrows near Crane Lake, Site 7

5/16/01 2.3 <0.1

8/21/01 0.2 <0.1

5/14/02 1.0 <0.1

8/21/02 3.0 <0.1

5/29/03 2.1 <0.1

Namakan Lake near Ray, Site 14 

5/16/01 2.0 <0.1

8/21/01 0.5 <0.1

5/14/02 2.1 <0.1

8/21/02 1.9 <0.1

5/29/03 1.4 <0.1

Rainy Lake at Brule Narrows near International Falls, Site 5

5/15/01 3.6 E0.1

8/20/01 1.0 <0.1

5/13/02 1.1 <0.01

8/20/02 1.2 <0.1

5/28/03 1.1 <0.1

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11

5/16/01 3.2 <0.1

5/30/01 1.2 <0.1

6/12/01 1.0 <0.1

6/25/01 2.9 <0.1

7/10/01 3.0 <0.1

7/24/01 4.8 <0.1

8/7/01 22.5 E0.3

8/21/01 4.4 <0.1

9/5/01 6.1 0.4

9/18/01 2.7 <0.1

10/2/01 2.8 <0.1

10/17/01 2.8 <0.1

5/14/02 2.7 <0.1

5/30/02 2.5 <0.1

6/12/02 1.2 <0.1

6/26/02 1.5 0.1

7/9/02 2.4 <0.1

7/23/02 3.6 <0.1

8/6/02 4.9 <0.1

8/21/02 22.1 <0.1

9/5/02 3.7 E0.5

9/17/02 E31.2 <0.1

9/30/02 22.8 <0.1

10/16/02 2.7 <0.1

5/14/03 2.7 <0.1

5/29/03 0.8 <0.1

6/10/03 1.4 <0.1

6/24/02 1.3 <0.1

7/8/03 1.6 <0.1

Table 11. Chlorophyll analyical results by site, Voyageurs National Park, Minnesota, 2001-03

[all units in micrograms per liter; E, estimated; <, less than]
Date Chlorophyll-a Chlorophyll-b

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11—Continued

7/22/03 4.1 <0.1

8/5/03 E3.2 <0.1

8/19/03 E8.9 <0.1

9/3/03 E7.5 <0.1

9/17/03 E7.8 <0.1

Kabetogama Lake at Cemetary Island near Ray, Site 43 

5/17/01 2.1 <0.1

5/31/01 E1.6 <0.1

6/12/01 0.9 <0.1

6/26/01 1.9 <0.1

7/10/01 3.2 <0.1

7/24/01 3.0 <0.1

8/7/01 11.1 E0.2

8/22/01 19.4 <0.1

9/5/01 6.8 <0.1

9/18/01 9.0 0.2

10/2/01 7.0 <0.1

10/17/01 2.1 <0.1

5/14/02 6.6 <0.1

5/30/02 0.7 <0.1

6/12/02 0.4 <0.1

6/26/02 2.5 0.3

7/9/02 4.5 <0.1

7/23/02 5.1 <0.1

8/6/02 23.7 <0.1

8/21/02 4.9 <0.1

9/5/02 7.7 E0.4

9/17/02 E4.3 <0.1

9/30/02 7.0 <0.1

10/16/02 1.5 <0.1

5/14/03 1.7 <0.1

5/29/03 0.7 <0.1

6/10/03 0.9 <0.1

6/24/03 2.3 <0.1

7/8/03 3.4 <0.1

7/22/03 3.1 <0.1

8/5/03 3.5 <0.1

8/19/03 E13.0 <0.1

9/3/03 21.0 <0.1

9/17/03 7.6 <0.1

Kabetogama Lake near Grave Island near Ray, Site 45 

5/17/01 3.5 <0.1

5/31/01 2.0 <0.1

6/12/01 1.3 <0.1

6/26/01 2.1 <0.1

7/10/01 3.0 <0.1

7/24/01 3.6 <0.1

Table 11. Chlorophyll analyical results by site, Voyageurs National Park, Minnesota, 2001-03—Continued

Appendix 37
38 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date Chlorophyll-a Chlorophyll-b

Kabetogama Lake near Grave Island near Ray, Site 45—Continued 

8/7/01 17.6 E0.2

8/22/01 21.4 <0.1

9/5/01 9.5 0.4

9/18/01 5.4 0.2

10/2/01 <0.1 <0.1

10/17/01 1.9 <0.1

5/14/02 2.2 <0.1

5/30/02 1.9 <0.1

6/12/02 1.7 <0.1

6/26/02 1.5 0.1

7/9/02 3.9 <0.1

7/23/02 5.2 <0.1

8/6/02 26.5 <0.1

8/21/02 7.6 <0.1

9/5/02 10.7 E1.0

9/17/02 E21.1 E0.1

9/30/02 67.3 <0.1

10/16/02 4.5 <0.1

5/14/03 2.1 <0.1

5/29/03 1.3 <0.1

6/10/03 0.9 <0.1

6/24/03 2.1 <0.1

7/8/03 2.8 <0.1

7/22/03 4.2 <0.1

8/5/03 E2.9 <0.1

8/19/03 E6.6 <0.1

9/3/03 E3.4 <0.1

9/17/03 E9.9 <0.1

Rainy Lake at Black Bay Narrows near International Falls, Site 1

5/15/01 2.6 <0.1

5/29/01 1.5 <0.1

6/11/01 1.1 <0.1

6/25/01 3.2 <0.1

7/9/01 14.9 E0.2

7/23/01 12.5 <0.1

8/6/01 E2.6 E0.1

8/20/01 4.7 0.3

9/4/01 3.1 0.4

9/17/01 3.4 <0.1

10/1/01 4.8 0.2

10/16/01 5.5 <0.1

5/13/02 8.0 <0.1

5/28/02 2.0 <0.1

6/11/02 1.0 <0.1

6/24/02 3.3 0.2

7/8/02 2.6 <0.1

7/22/02 13.2 0.9

8/5/02 5.6 1.1

8/20/02 4.3 0.5

Table 11. Chlorophyll analyical results by site, Voyageurs National Park, Minnesota, 2001-03—Continued
Date Chlorophyll-a Chlorophyll-b

Rainy Lake at Black Bay Narrows near International Falls, Site 1—Continued

9/4/02 5.7 E0.7

9/16/02 E5.0 <0.1

10/2/02 12.9 <0.1

10/15/02 2.4 <0.1

5/13/03 3.3 <0.1

5/28/03 1.4 <0.1

6/9/03 1.5 0.1

6/23/03 3.6 0.2

7/7/03 5.0 0.2

7/21/03 3.6 <0.1

8/4/03 E11.0 <0.1

8/18/03 E8.9 <0.1

9/2/03 E2.2 <0.1

9/15/03 E4.4 E0.2

Rainy Lake at Black Bay near International Falls, Site 16 

5/15/01 2.7 <0.1

5/29/01 1.4 <0.1

6/11/01 0.9 <0.1

6/25/01 1.8 <0.1

7/9/01 8.5 <0.1

7/23/01 8.5 <0.1

8/6/01 19.7 E0.3

8/20/01 2.9 <0.1

9/4/01 5.3 0.2

9/17/01 1.6 <0.1

10/1/01 6.5 0.2

10/16/01 5.4 E0.1

5/13/02 7.4 <0.1

5/28/02 1.5 <0.1

6/11/02 1.8 <0.1

6/24/02 1.8 0.2

7/8/02 2.4 <0.1

7/22/02 21.9 1.3

8/5/02 6.9 <0.1

8/20/02 7.8 <0.1

9/4/02 27.2 0.8

9/16/02 E17.3 <0.1

10/2/02 3.5 <0.1

10/15/02 2.8 <0.1

5/13/03 4.1 <0.1

5/28/03 2.6 <0.1

6/9/03 1.5 0.1

Rainy Lake at Black Bay (West) near International Falls, Site 44

5/15/01 1.8 <0.1

5/29/01 E0.7 <0.1

6/11/01 1.0 <0.1

6/25/01 1.3 <0.1

7/9/01 4.2 E0.2

Table 11. Chlorophyll analyical results by site, Voyageurs National Park, Minnesota, 2001-03—Continued

Appendix 39
40 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date Chlorophyll-a Chlorophyll-b

Rainy Lake at Black Bay (West) near International Falls, Site 44—Continued

7/23/01 13.2 <0.1

8/6/01 0.9 0.1

8/20/01 7.1 0.4

9/4/01 2.7 0.5

9/17/01 4.7 <0.1

10/1/01 5.9 0.2

10/16/01 5.6 E0.1

5/13/02 3.0 <0.1

5/28/02 1.2 <0.1

6/11/02 2.0 <0.1

6/24/02 1.6 0.1

7/8/02 2.1 E0.2

7/22/02 6.0 1.1

8/5/02 9.7 1.4

9/4/02 3.8 E0.5

9/16/02 E47.8 <0.1

10/2/02 3.4 <0.1

10/15/02 3.0 <0.1

5/13/03 3.2 <0.1

5/28/03 1.6 <0.1

6/9/03 2.3 <0.10

6/23/03 2.6 0.2

7/7/03 5.4 0.5

7/21/03 14.0 <0.1

8/4/03 17.0 <0.1

8/18/03 E13.0 <0.1

9/2/03 E3.8 <0.1

9/15/03 E3.2 E0.1

Table 11. Chlorophyll analyical results by site, Voyageurs National Park, Minnesota, 2001-03—Continued
Date

Chlorphyll-a

 (μg/L)

Total Phosphorus 

(mg/L)

Sand Point Lake below Harrison Narrows near Crane Lake, Site 7

5/14/02 1.3 0.0

5/30/02 5.3 0.0

6/12/02 4.9 0.0

6/25/02 2.7 0.0

7/9/02 1.0 0.0

7/23/02 0.2 0.0

8/6/02 0.9 0.0

8/21/02 0.3 0.0

9/5/02 3.3 0.0

9/17/02 2.4 0.0

9/30/02 1.6 0.0

10/17/02 1.5 0.0

5/14/03 5.5 0.0

6/10/03 2.3 0.0

6/24/03 1.5 0.0

7/8/03 0.5 0.0

7/23/03 0.7 0.0

8/5/03 0.5 0.0

8/19/03 2.7 0.0

9/4/03 3.6 0.0

9/19/03 2.3 0.0

9/29/03 3.9 0.0

Namakan Lake near Ray, Site 14

5/14/02 1.7 0.0

5/30/02 4.0 0.0

6/12/02 2.8 0.0

6/25/02 1.2 0.0

7/9/02 2.0 0.0

7/23/02 1.0 0.0

8/6/02 1.7 0.0

8/21/02 3.2 0.0

9/5/02 0.9 0.0

9/17/02 1.2 0.0

9/30/02 1.8 0.0

10/17/02 1.5 0.0

5/14/03 2.3 0.0

6/10/03 2.5 0.0

6/24/03 3.1 0.0

7/8/03 0.1 0.0

7/22/03 0.4 0.0

8/5/03 0.6 0.0

8/19/03 2.9 0.0

9/4/03 2.8 0.0

9/19/03 2.8 0.0

9/29/03 3.1 0.0

Table 12. Chlorophyll-a and total phosphorus analytical results determined for water samples in Voyageurs National Park, Minnesota by 

the Natural Resource Research Institute, 2002-03.

[μg/L, micrograms per liter; mg/L, milligrams per liter]

Appendix 41
42 Effects of Changes in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park 

Date

Chlorphyll-a

 (μg/L)

Total Phosphorus 

(mg/L)

Rainy Lake at Brule Narrows near International Falls, Site 5

5/13/02 1.3 0.0

5/28/02 1.5 0.0

6/11/02 1.7 0.0

6/24/02 2.0 0.0

7/8/02 0.8 0.0

7/24/02 1.0 0.0

8/5/02 0.2 0.0

8/20/02 1.8 0.0

9/4/02 0.9 0.0

9/16/02 2.2 0.0

10/2/02 2.3 0.0

10/17/02 1.6 0.0

5/13/03 2.5 0.0

6/9/03 2.8 0.0

6/23/03 0.9 0.0

7/7/03 0.4 0.0

7/21/03 0.6 0.0

8/4/03 0.7 0.0

8/18/03 1.4 0.0

9/2/03 2.3 0.0

9/15/03 3.9 0.0

9/28/03 2.4 0.0

Kabetogama Lake at Mouth of Meadwood Bay near Ray, Site 11

6/21/03 1.7 0.0

9/29/03 10.2 0.0

Kabetogama Lake at Cemetary Island near Ray, Site 43

6/20/03 2.8 0.0

9/29/03 6.0 0.1

Kabetogama Lake near Grave Island near Ray, Site 45

6/20/03 1.8 0.0

9/29/03 3.5 0.0

Rainy Lake at Black Bay Narrows near International Falls, Site 1

9/28/03 7.0 0.1

Rainy Lake at Black Bay (West) near International Falls, Site 44

9/28/03 11.2 0.2

Table 12. Chlorophyll-a and total phosphorus analytical results determined for water samples in Voyageurs National Park, Minnesota by 

the Natural Resource Research Institute, 2002-03.—Continued.
Christensen, and others—Effects of Change in Reservoir Operations on Water Quality and Trophic-State Indicators in Voyageurs National Park, Northern 

Minnesota, 2001-03—Scientific Investivation Report 2004-5044

Printed on recycled paper