U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 063–03

July 2003

Why Study Lakes? An Overview of USGS Lake Studies 

in Wisconsin

By H. S. Garn, J. F. Elder, and D. M. Robertson, Lake Studies Team, U.S. Geological Survey, Wisconsin District 

Printed on recycled paper

Wisconsin Lakes – a Natural Treasure

Wisconsin’s 15,000 lakes are prominent features in its landscape and an important public resource. In the northern part of 

the State, the recent glaciation (ending about 10,000 years ago) 

created one of the densest clusters of lakes found anywhere 

in the world, containing lakes that occupy depressions in the 

glacial moraines and outwash deposits (fig. 1). This Northern 

Lakes and Forests Ecoregion contains more than 80 percent of 

the State’s lakes (Wisconsin Department of Natural Resources, 

2001). South of this ecoregion, there are fewer lakes, but they 

still are common. Usually situated in agricultural or urban landscapes, lakes in southern Wisconsin generally have higher levels 

of nutrients and alkalinity, and higher biological productivity 

than their northern counterparts. For most lakes in Wisconsin, 

phosphorus is the nutrient that limits algal growth 

(Lillie and Mason, 1983).

Lakes are highly valued for their recreational, 

aesthetic and scenic qualities, and the water they 

contain is one of the most treasured of our natural resources (fig. 2). Lakes constitute important 

habitats and food resources for a diverse array of 

fish, aquatic life, and wildlife, but lake ecosystems 

are fragile. Lake ecosystems can undergo rapid 

environmental changes, often leading to significant 

declines in their aesthetic, recreational, and aquatic 

ecosystem functions. Exposed to external effects 

from the atmosphere, their watersheds, and ground 

water, lakes are subject to change through time. 

Human activities can further accelerate the rates 

of change. If the causes of the changes are known, 

however, human intervention (lake-management 

practices) sometimes can control, or even reverse, 

detrimental changes.

Limnology (the study of lakes and other freshwater systems) is the science that can provide 

improved understanding of lake ecosystem 

dynamics and information that can lead to sound 

management policies. As more studies are conducted on a variety of lake systems, the accumulated information leads to the development of 

general concepts about how lakes function and 

respond to environmental changes.

The condition of a lake at a given time is the 

result of the interaction of many factors—its 

watershed, climate, geology, human influence, and 

characteristics of the lake itself. With constantly 

expanding databases and increased knowledge, limnologists and 

hydrologists are able to better understand problems that develop 

in particular lakes, and further develop comprehensive models 

that can be used to predict how lakes might change in the future.

While the development of a limnological database and 

knowledge is important, no amount of generalization can 

provide a full understanding or predict conditions of any particular lake. Each lake system is unique, and its dynamics can 

be understood only to a limited degree based on information 

from other lakes. Just as a physician would not diagnose an 

individual’s medical condition or prescribe treatment without 

a personal medical examination, a limnologist or hydrologist 

cannot accurately assess a lake system or suggest a management 

strategy without data and analysis from that particular lake and 

0

0 20 40 60 KILOMETERS

20 40 60 MILES

45 ̊ 

43 ̊ 

92 ̊ 

89 ̊ 

87 ̊ 

EXPLANATION

Hydrological data from

Wisconsin Department of

Natural Resources

Western Corn Belt Plains

Driftless Area

Southeastern Wisconsin Till Plains

North Central Hardwood Forests

Central Corn Belt Plains

Northern Lakes and Forests

Level III Ecoregion

Open water

City

County boundary

Geneva Lake

Delavan Lake

Powers Lake

Devils Lake

Fish Lake Okauchee Lake

Lake Winnebago

Long Lake Little St. Germain Lake

Lake

St. Croix

Lauderdale Lake

Rhinelander

Ashland

Rice Lake

Eau Claire

La Crosse

Madison

Wausau

Green Bay

Rhinelander

Ashland

Superior

Rice Lake

Eau Claire

La Crosse

Madison

Wausau

Kenosha

Milwaukee

Green Bay

Figure 1. General distribution of lakes in relation to ecoregions of Wisconsin (adapted 

from Omernik and others, 2000).
2 Why Study Lakes? An Overview of USGS Lake Studies in Wisconsin

its environment. The following are some of the most important 

basic factors that give unique character to each lake ecosystem.

• Climate – Temperature, wind, precipitation, and solar 

radiation all critically affect the lake’s hydrologic and 

chemical characteristics, and indirectly affect the composition of the biological community. Precipitation is the main 

factor affecting runoff and the delivery of nutrients and 

sediments. Temperature, wind, and energy from the sun 

affect lake stratification and mixing, plant growth, 

and evaporation.

• Atmospheric inputs – The surface of a lake is directly 

exposed to atmospheric inputs. Not only wet precipitation, 

but also dry particles, can be major sources of certain contaminants to a lake. Each lake also receives indirect atmospheric inputs by way of the runoff from its watershed.

• Geologic substrate and soils in the basin – The soil type 

affects the potential for runoff and erosion. The physical 

characteristics of the substrate determine the extent, nature, 

and quality of ground-water inflows and outflows. These 

are primary factors affecting the lake’s chemistry, because 

of transfers between water and sediments, and input of 

sediment, minerals, and nutrients from the watershed by 

runoff water flowing into the lake. 

• Physiography – The area, surface topography, existence 

of upstream lakes and wetlands, altitude, and land slope 

of the lake’s watershed affect surface-water runoff and the 

amount and nature of chemicals and sediments entering the 

lake. The physiography of the region affects the size of a 

lake’s watershed and ground-water contributing area. The 

boundaries of a lake watershed and ground-water contributing area may not necessarily coincide. Interactions with 

land use by people can appreciably change how these factors affect runoff and the export of nutrients and sediment.

• Land use – The type, location, extent, and history of 

land cover/land use (such as agriculture, rural, and urban 

developed areas) can greatly affect the quantity of surfacewater and ground-water inflows and outflows, as well as 

the amounts and types of sediment, nutrients and chemicals (natural or synthetic) that are transported into the lake 

from the watershed.

• Lake morphometry –Size, shape, and depth characteristics of a lake are critical in determining currents and 

mixing of the lake, as well as its thermal and chemical 

stratification characteristics.

Common Environmental Problems in Lakes 

and Probable Causes

Eutrophication is the natural process of physical, chemical, and biological changes (“aging”) associated with nutrient, 

organic matter, and silt enrichment of a lake. If the natural process is accelerated by human influences, it is termed “cultural” 

eutrophication. Lakes are subject to a variety of physical, chemical, and biological problems that can diminish their aesthetic 

beauty, recreational value, water quality, and habitat suitability. 

Among the most common lake problems, and the conditions 

that often occur with eutrophication are the following.

• Algal blooms – Extensive and rapid growth of planktonic 

(floating and suspended) algae, caused by an increased 

input of nutrients (primarily phosphorus, but occasionally 

can also be caused by nitrogen), is a common problem in 

lakes (fig. 3). Lakes normally undergo aging over timescales of centuries or thousands of years, but the process 

can be accelerated rapidly to only decades by human 

activities that cause increases in sedimentation and nutrient 

inflow to the lake. Accelerated eutrophication and excessive algal growth reduces water clarity, inhibits growth of 

other plants, and can lead to extensive oxygen depletion, 

accumulation of unsightly and decaying organic matter, 

unpleasant odors, and fish kills. 

• Sedimentation/turbidity – Increases in accumulation 

and/or resuspension of sediments can be a detriment to 

water quality and habitat for many aquatic species. Such 

events usually are caused by heavy rains that produce erosion and intense runoff, carrying heavy sediment loads into 

lakes. High winds, boating activity, and bottom-feeding 

fish, such as carp, may also resuspend bottom sediments 

and increase turbidity. 

Figure 2. Long Lake, in northern Wisconsin, is a natural resource with 

high water quality, valued for its recreational, aesthetic and scenic 

qualities.

Figure 3. Algal bloom and degraded water quality of a lake affected by 

nutrient enrichment.
• Oxygen depletion – Decreases in dissolved oxygen to 

less than 3 mg/L (milligrams per liter) in the water can 

be harmful or lethal to many desirable species of aquatic 

life. The primary mechanism of oxygen loss is consumption by high rates of respiration and organic decomposition. Ideally, such consumption is offset by oxygen inputs 

from the atmosphere and from photosynthesis by aquatic 

plants. However, in stratified lakes, the atmospheric source 

is cut off from the hypolimnion (deep lake layer), and 

oxygen concentrations in the hypolimnion may decline 

to zero (anoxia) until the lake mixes again. Under anoxic 

conditions, phosphorus may be released from the bottom 

sediments into the overlying water. This “internal loading” 

may be considerable with phosphorus-enriched sediments 

and prolonged anoxia. Prolonged low oxygen concentrations in the summer or under ice in the winter can lead to 

fish kills.

• Growth of aquatic plants (macrophytes) – Normal 

macrophytic growth generally is beneficial for the lake 

ecosystem; among other benefits, the plants provide refuge 

for fish and other organisms. However, in some lakes, the 

growth of aquatic plants (“weeds”) can become excessive 

and create a serious nuisance for lake users, interfering 

with swimming, boating, and other recreational activities. 

Excessive macrophytes commonly are caused by increased 

nutrients, invasion of exotic species, or accumulation of 

organic sediment. The improvement of water clarity resulting from management actions designed to control algal 

production can provide better conditions for growth of 

rooted plants.

• Water-level changes – Wide fluctuations in stage (lake 

level) can create major hardships for lakeside residences, 

marinas, and businesses, and they also may impair the 

habitat suitability for nearshore biota. These changes most 

commonly are linked to weather anomalies (extended periods of abnormally high or low precipitation), but also may 

be associated with human activities such as withdrawals 

for water use.

• Species shifts – Populations of desirable animal and plant 

species might decline sharply or disappear, to be replaced 

by other species. Usually, the new dominant species will 

become a nuisance and degrade some or all desirable qualities of the lake. Species shifts can be caused by introduction of invasive species that may have little or no natural 

controls on their population growth, or are stimulated by 

changes in environmental conditions (for example, climate 

changes, acidification from “acid rain” or other changes in 

water chemistry, or physical changes). 

To diagnose or identify causes of problems, one must understand the processes and interactions within the lake (among its 

morphometry, water quality, algae, macrophytes, fish, and other 

fauna) and those between the lake and its watershed (quantity 

and quality of inputs from precipitation, surface water, ground 

water, and other localized sources). A combination of natural 

factors within the watershed and the lake may be acting to produce a fertile lake, and there may be little opportunity to improve 

its water-quality condition by management actions. However, if 

human activities and developments creating hydrologic modifications or increasing sediment and nutrient inputs are the 

cause of accelerated eutrophication, then these effects may be 

reduced by management measures in the watershed and (or) the 

lake. Qualitative and quantitative limnological and hydrological investigations can help to differentiate between natural and 

human-caused problems and to identify possible solutions.

Purposes, Objectives, and Design of Lake Studies

Lake studies are conducted to meet specific purposes, or 

combinations of purposes, that support management activities 

and decisions made by a lake association, lake district, or other 

private or governmental organizations. Among the most common of these purposes are as follows. 

• Development and implementation of lake-management 

plans

• Protection of present water quality

• Restoration of former water quality

• Watershed (land-use) planning and management

• Wetland protection or restoration

• Lake classification and local ordinance development

• Protection of fish and wildlife and their habitats

The success of any lake study depends on development of 

appropriate objectives, based on careful attention to the overall 

purpose(s) of the study. A study plan, selection of methods, 

and a data-collection program for the lake and its watershed 

then can be developed to acquire the information necessary to 

achieve these objectives. Objectives of lake studies generally 

include one or more of the following.

• Assess current physical, chemical, and biological conditions 

• Determine how conditions are changing with time

• Assess watershed characteristics (hydrology, water 

quality, land uses, nutrient and sediment yields, and 

sources of nutrients)

• Identify problems and opportunities for lake improvement

• Determine causes of lake problems, and provide information that can be used to design management actions, if any, 

that are feasible and likely to be successful in treating the 

lake’s problems

• Evaluate the effectiveness of implemented management 

measures and determine whether they are performing as 

planned

Lake studies vary considerably in the amount and detail of 

information gathered. The design of the study depends on its 

purpose and objectives. Decisions about the types and frequency 

of data collection should be made based on a cost/benefit 

assessment of each item—do these data contribute to fulfillment 

of the purpose and are their contributions sufficient to justify 

the cost and effort of collecting them? The accuracy of results 

needed from the study and the methods to be used (whether to 

Common Environmental Problems in Lakes and Probable Causes 3
4 Why Study Lakes? An Overview of USGS Lake Studies in Wisconsin

rely on estimated rather than measured data) depend on the type 

and severity of problems, and the social and economic effects of 

decisions (management actions) that need to be made to address 

the problems.

Types of Lake Studies

Lake studies by the U.S. Geological Survey (USGS), Wisconsin District Lake Studies Team are conducted to achieve 

many of these objectives, and generally fall into various levels 

or types of studies, from simple to complex (summarized in 

table 1). Each level grades to the next and may include components of the type of study done in the lower levels, as well 

as additional investigations. The Team’s mission is to provide 

hydrologic, water quality, and other scientific information to 

help describe current characteristics and conditions of lakes, 

help identify and understand problems, and help determine 

effective management actions to protect or restore lakes in 

Wisconsin and the Nation. Information about the Wisconsin 

District Lakes Program can be found at http://wi.water.usgs.gov/

projects/index.html. Nationally consistent laboratory procedures 

and quality control are used by the USGS in conducting these 

studies. The standards ensure that all data are directly comparable from region to region in the country, and available from 

national USGS databases.

Monitoring Studies

Studies to assess current conditions and trends may be 

referred to as monitoring studies because they usually entail 

collection of data (monitoring), but little or no investigation of 

causes of problems, processes, or ecosystem dynamics. Whether 

the study involves monitoring of only lake stage, or a range of 

chemical and biological variables, it essentially is an informational study. Monitoring may include review and evaluation 

of available data, lake-level monitoring, and monitoring of 

in-lake physical, chemical, and biological variables useful for 

describing the condition (typically trophic status) of the lake, 

and comparing trophic state indicies (Carlson, 1977) with other 

lakes in the region. Interpretation of the data generally is limited 

to analysis of in-lake characteristics and possibly trends (how 

the variables might be changing over time) if sufficient data are 

available. Long-term data collection (greater than 5 years), using 

Table 1. General summary of the types of lake studies and approaches 

used by the USGS Wisconsin District Lake Studies Team to address 

study objectives

Monitoring studies

Objective: Assess current conditions and evaluate trends

Approach: Monitoring by USGS, volunteers (self-help), 

State or other agencies; compare with other available 

data.

Diagnostic studies

Objective: Identify causes of problems

Approaches:

A. Qualitative and semi-quantitative evaluation of 

sources of problems. Use limited monitoring and data from 

other studies, compute water and nutrient budgets from 

estimated data.

B. Quantitative evaluation of sources of problems. 

Monitoring measures major components of water and 

nutrient budgets to provide greater resolution of sources 

and causes.

Feasibility studies

Objective: Evaluate feasibility of possible solutions and 

effectiveness of management practices

Approach: Incorporate many activities from the diagnostic approach above plus evaluation of likely solutions. 

Monitor and evaluate the effectiveness of improvement 

measures.

Table 2. Commonly measured variables for monitoring lakes, and usual 

depth intervals where sampled

[NS, near surface; NB, near bottom; profile, multiple depths at one site, from 

surface to bottom; Sed, in bottom sediments; TSI, trophic state index; A, as 

appropriate for species sampled]

Variable Depth

1. Water level (stage) water surface

2. Common field and TSI variables:

 A. Water transparency

 (Secchi depth, light penetration)

NS

 B. Water temperature profile

 C. Dissolved oxygen profile

 D. pH (acidity) profile

 E. Specific conductance profile

 F. Chlorophyll1

 NS

3. Chemical variables:

 A. Nutrients (phosphorus, nitrogen) NS, NB, intermediate

 B. Major cations and anions NS/NB

 C. Organic carbon NS/NB, Sed

 D. Synthetic organic compounds NS/NB, Sed

 E. Trace elements, metals NS/NB, Sed

4. Ecological/biological variables

 A. Phytoplankton (algae/floating plants) NS

 B. Macrophytes

 (plants rooted in lake bottom)

near-shore area

 C. Primary productivity2

 NS

 D. Attached algae bottom

 E. Benthic organisms

 (bottom-dwelling animals)

NB/Sed

 F. Zooplankton

 (small animals, usually crustaceans, 

 in water)

A

 G. Fish A

1

 usually chlorophyll a (Chl a) – a measure of density and activity of algae 2

 primary productivity (PPR) – a measure of photosynthesis; (less common 

measurement than Chl a)
consistent and comparable methods, is critical for differentiating 

real trends from short-term climatic fluctuations. Trend analysis becomes continually more meaningful and valuable as the 

length of time of monitoring increases.

Stage (lake-level) monitoring. This kind of data collection 

involves monitoring of water level (stage) of the lake, and how 

it changes over time. Stage monitoring also is used to determine 

changes in volume of lakes when computing water budgets. 

These data can be readily and accurately obtained with a staff 

gage read by an observer, or a stage recorder, which enables 

automatic collection of continuous data at frequent preset time 

intervals. It is particularly important to maintain the same datum 

over the period of record at a gage. Devils Lake in Sauk County, 

and Fish Lake in Dane County are examples of lakes that have 

been in this program for many years (Wisconsin District Lake 

Studies Team, 2002).

In-lake water-quality monitoring. This effort routinely 

involves collection of data on physical, chemical, and biological 

variables at intervals during the year. Sampling times for most 

lakes are commonly during late winter (to determine conditions 

under ice cover), at spring overturn when the lake is mixed, and 

monthly during the summer (June through August). The list of 

variables to monitor and sampling frequencies may be modified 

for each lake, depending on the characteristics of the lake and 

problems experienced. 

Physical, chemical, and biological variables that may be 

monitored in lakes to fulfill certain study purposes are listed 

in table 2. Items 1, 2, 3A, and 3B in the table commonly are 

included in many lake monitoring studies. Depth profiles of 

field variables can be measured quickly on-site with multiparameter instruments. These variables are measured at closely 

spaced intervals (generally 0.5–1 meters depending on the 

depth of the lake) from the surface to the bottom, to determine 

changes in temperature, dissolved oxygen, pH, and specific conductance with water depth (figs. 4 and 5). Other variables that 

require collection of water samples and analyses in the laboratory, particularly chemical (such as phosphorus and nitrogen) 

and biological samples, commonly are sampled at two or more 

depths. 

The profile measurements and samples generally are taken 

at a representative site, located at or near the deepest part (the 

“deep hole”) of the lake. Additional monitoring may be done at 

other sites in strategic locations to characterize specific features 

of the lake system, such as inflows and outflows, multiple deep 

basins, or additional bays of complex-shaped lakes (Holdren, 

Jones, and Taggart, 2001). 

Data from these measurements and samples provide a basis 

for scientific assessment of lake condition and common lake 

problems. For example, profile data may show the extent of 

dissolved oxygen depletion over the summer, and nutrient data 

may identify high concentrations of available phosphorus for 

algal growth or phosphorus release from bottom sediments. 

Combined with data on water transparency (Secchi depth) and 

algal pigment (chlorophyll a), these data support calculation of 

the lake’s trophic state index (TSI) (fig. 6), which is a quantitative, objective measure of the current state of the lake in the 

eutrophication process. Okauchee Lake in Waukesha County 

is an example of a lake in this study type with long-term data. 

This lake has been monitored for water quality since 1984 

(Wisconsin District Lake Studies Team, 2002). About 100 lakes 

throughout the State have been monitored at this level by the 

USGS since mid-1980.

2-12-01 4-10-01 6-19-01 7-26-01 8-20-01

DISSOLVED OXYGEN CONCENTRATIONS (D.O.) IN MILLIGRAMS PER LITER

WATER TEMPERATURE (W.T.) IN DEGREES CELSIUS

DEPTH, IN METERS

0 10 20

0 10 20 30

0

3

6

12

9

0 10 20

0 10 20 30

0

3

6

12

9

0 10 20

0 10 20 30

0

3

6

12

9

0 10 20

0 10 20 30

0

3

6

12

9

0 10 20

0 10 20 30

0

3

6

12

9

W.T. W.T. D.O. D.O. D.O.

D.O.

D.O.

W.T. W.T. W.T.

Figure 5. Graphs showing typical profile data for water temperature and dissolved oxygen (Powers Lake, Kenosha County, Wis.).

Figure 4. Measurement 

of lake water-quality 

profiles with a multiparameter water-quality 

instrument.

Types of Lake Studies 5
6 Why Study Lakes? An Overview of USGS Lake Studies in Wisconsin

Diagnostic Studies

Studies to diagnose problems and identify possible solutions, 

generally termed diagnostic studies, extend beyond monitoring 

to include more complex data collection, analysis of the hydrologic system and processes, and interpretation. The objectives of 

these studies usually include quantifying the problems, defining causes of the problems, and identifying possible solutions. 

Results commonly are used in the development of lake-management plans. These studies usually include basic data collection, 

but the studies go further, to include searches for answers to 

questions such as: How severe are the problems? What are the 

major sources of nutrients and causes of the problems? What 

are the most likely solutions? 

Diagnostic studies commonly include activities that:

• monitor and quantify the major inflows to and outflows 

from the lake to develop a detailed water budget for the lake; 

• determine phosphorus and sediment loads associated 

with major water inflow and outflow source, and develop 

a detailed phosphorus budget for the lake, thereby 

providing a better understanding of the problems and 

sources of nutrients;

• evaluate lake water quality in relation to water and nutrient 

loading by the use of lake water-quality models, such as 

the Wisconsin Lake Modeling Suite, WiLMS (Panuska and 

Kreider, 2002).

Methods used in studies at this level vary greatly and may 

include both qualitative and quantitative methods based on 

estimates from the literature and previous studies, and on monitored data. Studies are designed to fit the hydrologic conditions, 

severity of problems, accuracy desired, and objectives of the 

study. Various components of the water and phosphorus budgets may be estimated or measured. Phosphorus usually is the 

nutrient that limits algal growth (Guildford and Hecky, 2000). 

Precipitation is measured by a recording rain gage or estimated 

from nearby National Weather Service station data. Phosphorus 

input from precipitation is estimated from published values. 

Evaporation usually is estimated from published evaporation 

values. Surface-water inflow and outflow may be determined by 

recording streamflow-gaging stations (fig. 7) near the mouths 

of major tributaries and at the lake outlet. Surface-water flows 

are sampled and analyzed for phosphorus and sediment concentrations. Streamflow data, along with the concentration data, 

are used to determine the annual phosphorus inputs and losses. 

Phosphorus input (load) from surface water may be estimated 

by a regression approach (Cohn and others, 1989; Robertson 

and Roerish, 1999) with limited concentration data collected 

manually, or may be computed more accurately by using an 

integration technique (Porterfield, 1972) with extensive concentration data from frequent water sampling by observers or automatic water samplers. Inflow from small unmonitored watershed 

areas usually is estimated through the use of runoff coefficients 

using data from the nearby gaged watersheds, or tributary loads 

may be estimated by applying unit-area loads from previously 

monitored small watersheds (Corsi and others, 1997).

Net ground-water flow to the lake may be calculated as the 

residual in the water-budget equation, or determined by analyzing water-level data from piezometers (small-diameter wells, 

usually 1 inch or less) installed around the periphery of the lake 

and applying a two-dimensional ground-water-flow model, such 

as GFLOW (Haitjema, 1995) to the area. Water from nearshore 

piezometers is sampled and analyzed to measure phosphorus 

concentrations in ground water and to determine the loading 

Trophic state index (TSI) for Okauchee Lake, 1984–2002

20

30

40

50

60

70

TSI UNITS

Summer total phosphorus at Okauchee Lake, 1984–2002

0.000

0.005

0.010

0.015

0.020

0.025

PHOSPHORUS CONCENTRATION,

IN MILLIGRAMS PER LITER

Chlorophyll a

Secchi depth

Phosphorus

Eutrophic

Mesotrophic

Oligotrophic

1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

1984 1986 1988 1990 1992 1994 1996 1998 2000 2002

Trend line

Figure 6. Total phosphorus and trophic state index (TSI) data for 

Okauchee Lake, Waukesha County, Wis., 1984–2002.

Figure 7. Typical U.S. Geological Survey recording streamflow-gaging 

station with automatic water sampler for load determinations.

W.J. Rose
from ground water. Data for the flows and loads from the various sources are then used to construct water and phosphorus 

budgets for the lake (fig. 8).

Qualitative and semi-quantitative study approaches to evaluate 

problems are appropriate for lakes with less-severe problems and 

lower-cost solutions, where less-accurate results may be adequate 

(table 1). Quantitative study approaches, where major water 

and nutrient-budget components are measured directly, provide 

greater accuracy of results but at a higher cost. These studies are 

more appropriate for lakes with severe, complex problems. Diagnostic studies may typically require 3 to 5 years to complete.

Information and data discussed above are essential for 

understanding lake problems, identifying major sources and the 

relative importance of nutrient inputs, and identifying effective 

management strategies that can be used for developing lake and 

watershed management plans. Examples of recently completed 

lake diagnostic studies are Muskellunge and Little St. Germain 

Lakes in Vilas County (Robertson and Rose, 2000; 2003), Lake 

St. Croix in western Wisconsin (Robertson and Lenz, 2002), 

and Lauderdale Lakes in Walworth County (Garn and others, 

1996). Diagnostic studies have been conducted by the USGS 

for about 25 lakes in Wisconsin.

Feasibility Studies

Studies to evaluate the feasibility and effectiveness of management measures, referred to as feasibility studies, go beyond 

diagnostic studies but generally incorporate many of the same 

activities. Studies include objectives similar to diagnostic studies, but also may include greater definition of the problems and 

causes, evaluation of solutions, and model simulation of future 

conditions. These lakes generally have more complex lake 

and watershed factors affecting water quality and usually have 

multiple or severe problems. Expensive restoration and protection measures often are being considered in such lakes, or they 

may already be in progress. These studies often are longer term 

than those for diagnostic studies, and may include monitoring to 

evaluate the effectiveness of implemented management measures (such as watershed practices that reduce nutrient loading, 

lake aeration, or treatment of bottom sediment). The studies 

may address questions such as: How has the lake changed in 

recent years or decades, and how do those changes relate to 

environmental changes, watershed characteristics, or land uses? 

What management measures would be most effective? Are 

treatments working as planned? What kinds of changes can be 

expected in the future? Various kinds of modeling techniques 

(watershed models, ground-water models, and lake models) may 

be applied to predict water-quality changes based on collected 

data and to evaluate the feasibility of solutions, thus providing 

information that can be used to design treatments. 

These studies commonly include the components of diagnostic studies, but additionally include activities that: 

• describe historical changes in lake water quality resulting 

from outside effects;

• relate the measured water and contaminant loads to 

observed and modeled water quality within the lake; and 

• apply a calibrated lake model to predict how potential 

increases or decreases in phosphorus loading may effect 

the trophic status of the lake. 

Lake water-quality models, such as BATHTUB (Walker, 

1996) or the Wisconsin Lake Modeling Suite, WiLMS (Panuska 

and Kreider, 2002) may be used to evaluate and predict lake 

water quality relative to different phosphorus-loading scenarios. 

Interpretation may include assessment of probable responses 

to increases or decreases in nutrient loading that might result 

from various development and management scenarios within the 

lake’s watershed, and prediction of probable outcomes of different management strategies. Lake studies at this level have been 

conducted at Delavan Lake (Robertson and others, 2000) and 

Geneva Lake in Walworth County (Robertson and others, 2002). 

Sources of Funding 

Two popular programs in Wisconsin that help fund lake studies are those of the Wisconsin Department of Natural Resources, 

Lake Planning and Protection Grant Program, (described at http:

//www.dnr.state.wi.us/org/water/fhp/lakes/lkgrants.htm) and the 

USGS Cooperative Water Program. State grants can provide 

up to 75-percent funding to lake districts, lake associations, 

and other qualified local organizations and agencies for lake 

planning and management activities; the remaining 25 percent 

of project cost is provided by the local agency or lake district. 

The USGS Cooperative Water Program is a long-standing 

partnership between USGS and State and local governments for 

funding data collection and water-resources studies. Under this 

program the USGS may provide matching funding presently up 

to 40 percent of the total cost of the study to collect hydrologic 

data and conduct investigations, in cooperation with any local 

or State agency. 

Water budget

Precipitation Evaporation Surface-water

inflow

Surface-water

inflow

Surface-water

outflow

Surface-water

outflow

Net

ground water

Ground water

Change in

storage

Phosphorus budget

-2,000

-1,500

-1,000

-500

0

500

1,000

1,500

2,000

Precipitation Septic 

systems

Deposition

in lake

WATER INPUTS AND LOSSES, IN ACRE-FEET PHOSPHORUS INPUTS AND LOSSES, IN POUNDS

-15,000

-12,000

-9,000

-6,000

-3,000

0

3,000

6,000

9,000

1997

1999

1997

1999

Figure 8. Hydrologic and phosphorus budgets of Little St. Germain Lake, 

Wis., 1997 and 1999 (from Robertson and Rose, 2000).

Types of Lake Studies 7
8 Why Study Lakes? An Overview of USGS Lake Studies in Wisconsin

Lake Studies – an Investment for the Future 

Preservation of our lakes for their beauty and recreational 

benefits, as well as for their value as habitats for fish and wildlife, is of paramount importance. During the past century, our 

understanding of lakes has advanced considerably. Whereas we 

once were relatively unaware of the sensitivity of lakes to disturbances within their basins and watersheds, we are now much 

more alert to this sensitivity, and, consequently, we are more 

careful about actions that could accelerate lake deterioration. 

Lake studies, which contribute to general and specific knowledge of lake systems, require commitment of considerable effort 

and funding, but this commitment leads to major improvement 

of the likelihood of developing successful lake-management 

strategies and avoiding costly problems in the future. The goal 

of lake monitoring is to identify small changes in conditions so 

that remedial work can start before a lake has degraded extensively and expensive restoration measures are necessary. Lake 

monitoring is an investment for the future with potential for 

high returns.

“The future water quality of Wisconsin’s lakes lies in the 

wise management of our natural resources. Shoreline and landuse management, nonpoint-source pollution control, and control 

of toxic wastes are all critically important elements in protecting Wisconsin’s many lakes.” (Lillie and Mason, 1983)

Acknowledgments

The authors thank colleague reviewers P.J. Garrison and P.W. 

“Buzz” Sorge, Wisconsin Department of Natural Resources, 

and W.J. Rose, U.S. Geological Survey for their helpful review 

comments.

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