Lake Onalaska, Lower Black River,Lower La Crosse River Watershed (BL04)
Lake Onalaska, Lower Black River,Lower La Crosse River Watershed (BL04)
Lake Onalaska (728100)
8391.35 Acres
Natural Community
Natural communities (stream and lake natural communities) represent model results that use predicted flow and temperature based on landscape features and related assumptions. Ranges of flow and temperature associated with specific aquatic life communities (fish, macroinvertebrates) help biologists identify appropriate resource management goals. Wisconsin Natural Communities.
Shallow Lowland
Year Last Monitored
This is the most recent date of monitoring data stored in SWIMS. Additional surveys for fish and habitat may be available subsequent to this date.
La Crosse
Trout Water 
Trout Waters are represented by Class I, Class II or Class III waters. These classes have specific ecological characteristics and management actions associated with them. For more information regarding Trout Classifications, see the Fisheries Trout Class Webpages.
Outstanding or Exceptional 
Wisconsin has designated many of the state's highest quality waters as Outstanding Resource Waters (ORWs) or Exceptional Resource Waters (ERWs). Waters designated as ORW or ERW are surface waters which provide outstanding recreational opportunities, support valuable fisheries and wildlife habitat, have good water quality, and are not significantly impacted by human activities. ORW and ERW status identifies waters that the State of Wisconsin has determined warrant additional protection from the effects of pollution. These designations are intended to meet federal Clean Water Act obligations requiring Wisconsin to adopt an 'antidegradation' policy that is designed to prevent any lowering of water quality - especially in those waters having significant ecological or cultural value.
Impaired Water 
A water is polluted or 'impaired' if it does not support full use by humans, wildlife, fish and other aquatic life and it is shown that one or more of the pollutant criteria are not met.

Fish and Aquatic Life

Current Use
The use the water currently supports. This is not a designation or classification; it is based on the current condition of the water. Information in this column is not designed for, and should not be used for, regulatory purposes.
Shallow Lowland
Shallow lowland lake describes the depth and location of the lake in a watershed. These variables affect the lakes response to watershed variables.
Attainable Use
The use that the investigator believes the water could achieve through managing "controllable" sources. Beaver dams, hydroelectric dams, low gradient streams, and naturally occurring low flows are generally not considered controllable. The attainable use may be the same as the current use or it may be higher.
Fish and Aquatic Life - waters that do not have a specific use designation subcategory assigned but which are considered fishable, swimmable waters.
Designated Use
This is the water classification legally recognized by NR102 and NR104, Wis. Adm. Code. The classification determines water quality criteria and effluent limits. Waters obtain designated uses through classification procedures.
Default FAL
Fish and Aquatic Life - Default Waters do not have a specific use designation subcategory but are considered fishable, swimmable waters.


Lake Onalaska is a shallow headwater backwater of the Mississippi River that covers over eight thousand acres. The lake was last monitored in 2010, but its general condition remains unknown.

Date  2011

Author   Aquatic Biologist

Lake Onalaska, Lower Black River,Lower La Crosse River Watershed (BL04) Fish and Aquatic LifeLake Onalaska, Lower Black River,Lower La Crosse River Watershed (BL04) RecreationLake Onalaska, Lower Black River,Lower La Crosse River Watershed (BL04) Fish Consumption

General Condition

This 7,700 acre lake is bounded by Lock and Dam 7 on the south, Wisconsin on the east, the Black River delta to the north, and barrier islands which define the navigation channel of the Mississippi River on the west. The lake receives flow from both the Mississippi and Black Rivers. Halfway Creek also discharges to the northeastern part of the lake. The U.S. Corp of Engineers restricted the Mississippi River inflow to the lake to help maintain the navigation channel. Lake Onalaska management issues are dealt with by the Mississippi-Lower St. Croix Team within the WDNR and several federal agencies.

The northeastern shoreline of Lake Onalaska contains many homes. The nearshore area of the lake was historically dredged to move logs easily from the mouth of the Black River to the City of La Crosse. Dredging has not occurred in this portion of the lake for over 20 years. This Brice Prairie channel has become more shallow over the years and surface water flows have changed due to sedimentation patterns. Excessive algae blooms occur in this channel during the summer months (Endris). A winter survey of the Brice Prairie channel in February 1997 revealed elevated levels of nitrate plus nitrite nitrogen. This channel is influenced by groundwater inflows which result in relatively warm water conditions in this channel during the winter months. The source of these nutrients may be originating from several sources including the Onalaska landfill, septic systems and manure and fertilizer applications on nearby agricultural fields (Sullivan). The Town of Onalaska, Onalaska Lake District, and major industries in the Brice Prairie area should re-examine sewering all or portions of the Brice Prairie. Lakeside residents would like to see some improvement to the water quality conditions in this channel.

One aquatic plant which is vital to the canvasback duck is Vallisneria sp., also known as wild celery. Lake Onalaska at one time contained vast quantities of this plant species and was an important migration stop for the canvasback. As the worldwide population of canvasbacks shrank drastically, the Mississippi River flyway contained the last stable population. When the decline of the wild celery populations occurred after a number of drought years (1987-89), many were concerned about the demise of the canvasbacks. A systemwide reduction of plant species occurred at the same time. It is theorized that low flows during the drought years reduced the nitrogen available to submergent aquatic plants via lower concentrations and competition with algae for nitrogen and light. Several years of low flow with reduced available nutrients stressed plants enough to cause their decline. Subsequent normal flow years produced higher suspended sediment concentrations than expected, which reduced light penetration. For the submergent aquatic plants to rebound and thrive, proper amount of nutrients, light penetration, flow, and other factors must exist. The aquatic plant community of Lake Onalaska and the Upper Mississippi River has shown improvements in the extent of the submergent aquatic plant community since the drought years between 1987-89. Fluctuation of plant populations occur from year to year, but three consecutive drought years resulted in more severe conditions and a longer recovery time for the aquatic plants (Sullivan, 1999).

Three islands were constructed in Lake Onalaska in 1989 to reduce wave re-suspension of fine sediments, provide predator free nesting and loafing sites for waterfowl, and aid in the re-establishment of aquatic vegetation beds. Each crescent shaped island is approximately 3.5 acres in size and provides areas of diverse lake habitat that didn't previously exist within the shallow lake. Signs of increasing use by nesting waterfowl have been noted on the relatively predator free islands. An increase of aquatic vegetation has been documented throughout the lake. The protected areas downstream of the islands may be experiencing an accelerated rate of re-vegetation (Janvrin). Other areas of the river are also seeing an improvement in aquatic vegetation.

Date  2000

Author   Aquatic Biologist


Wisconsin has over 84,000 miles of streams, 15,000 lakes and milllions of acres of wetlands. Assessing the condition of this vast amount of water is challenging. The state's water monitoring program uses a media-based, cross-program approach to analyze water condition. An updated monitoring strategy (2015-2020) is now available. Compliance with Clean Water Act fishable, swimmable standards are located in the Executive Summary of Water Condition in 2018. See also the 'monitoring and projects' tab.


Management Goals

Wisconsin's Water Quality Standards provide qualitative and quantitative goals for waters that are protective of Fishable, Swimmable conditions [Learn more]. Waters that do not meet water quality standards are considered impaired and restoration actions are planned and carried out until the water is once again fishable and swimmable

Management goals can include creation or implementation of a Total Maximum Daily Load analysis, a Nine Key Element Plan, or other restoration work, education and outreach and more. If specific recommendations exist for this water, they will be displayed below online.


Monitoring the condition of a river, stream, or lake includes gathering physical, chemical, biological, and habitat data. Comprehensive studies often gather all these parameters in great detail, while lighter assessment events will involve sampling physical, chemical and biological data such as macroinvertebrates. Aquatic macroinvertebrates and fish communities integrate watershed or catchment condition, providing great insight into overall ecosystem health. Chemical and habitat parameters tell researchers more about human induced problems including contaminated runoff, point source dischargers, or habitat issues that foster or limit the potential of aquatic communities to thrive in a given area. Wisconsin's Water Monitoring Strategy was recenty updated.

Grants and Management Projects

Monitoring Projects

Watershed Characteristics

Lake Onalaska is located in the Lower La Crosse River watershed which is 145.46 miĀ². Land use in the watershed is primarily forest (42.30%), agricultural (14.80%) and a mix of urban (10.30%) and other uses (32.50%). This watershed has 295.20 stream miles, 1,187.12 lake acres and 5,641.64 wetland acres.

Nonpoint Source Characteristics

This watershed is ranked Medium for runoff impacts on streams, Not Ranked for runoff impacts on lakes and Low for runoff impacts on groundwater and therefore has an overall rank of Low. This value can be used in ranking the watershed or individual waterbodies for grant funding under state and county programs.This water is ranked High Lake for individual Lakes based on runoff problems and the likelihood of success from project implementation.

Natural Community

Lake Onalaska is considered a Shallow Lowland under the state's Natural Community Determinations.

Natural communities (stream and lake natural communities) represent model resultsand DNR staff valiation processes that confirm or update predicted conditions based on flow and temperature modeling from historic and current landscape features and related variables. Predicated flow and temperatures for waters are associated predicated fish assemblages (communities). Biologists evaluate the model results against current survey data to determine if the modeled results are corect and whether biological indicators show water quaity degradation. This analysis is a core component of the state's resource management framework. Wisconsin's Riverine Natural Communities.

Shallow lowland lake describes the depth and location of the lake in a watershed. These variables affect the lakes response to watershed variables.

Fisheries & Habitat

Loss of fish habitat, specifically for centrarchids (sunfish), due to excessive aquatic vegetation and sedimentation was documented around the mouth of Halfway Creek and Rosebud Island within Lake Onalaska. Large fluctuations in dissolved oxygen were caused by the photosynthetic and respiratory activity of submerged aquatic plants, with periods of near anoxic conditions (Schellhaass & Sullivan 1987b) A portion of the lake was dredged near Rosebud Island in 1989 to create more fishery habitat. The dredge spoils from this project were used to create three islands and transported inland as fill for a highway project. Dissolved oxygen concentrations have improved following the dredging project as a result of increased flows through the dredge cut channel. However, flows were initially too high and resulted in unfavorable velocity and cold temperatures in the dredge cut during winter months. (Sullivan and others, 1993). Flow modifications at the Onalaska Spillway, a part of navigation Pool 7 control structure, were initiated following the reconstruction of the spillway in 1994-95. Winter flows have been reduced and has resulted in improved velocity and thermal conditions for centrarchids (Sullivan).

Date  2000

Author   Aquatic Biologist