Cox Hollow Lake, Mill and Blue Mounds Creek Watershed (LW15)
Cox Hollow Lake, Mill and Blue Mounds Creek Watershed (LW15)
Cox Hollow Beach - Gov Dodge SP, Cox Hollow Lake (1246500)
0.05 Miles
0 - 0.05
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.
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.
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.
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.

Historical Description

Source: 1968, Surface Water Resources of Iowa County,WI: WI-DNR Cox Hollow Lake, T6N, R4E, Section 10, 11

Cox Hollow Lake is an impoundment of the headwaters of Mill Creek whose primary water sources are seepage and runoff. It lies wholly within the 4,600-acre Governor Dodge State Park and was constructed in 1958. The primary use is for wildlife and recreation but it also serves as a flood control device in conjunction with the Twin Parks Watershed flood control project on the Mill Creek system. There is a 25-foot high dam which maintains about a 20-foot head throughout the year. The fishery was created by stocking. Originally it was managed for largemouth bass, northern pike and bluegills but during the past few years its fishery has deteriorated to largemouth bass and a large population of stunted bluegills. Other species which are present include white suckers, black bullheads and various forage fishes. Currently, there is a serious weed problem which interferes with recreational use. For the past three years the Bureau of Research has conducted a study involving the use of aero-hydraulic guns to circulate seasonally stratified waters and follow limnological and biological changes which have resulted. Game assets include a sizable population of muskrats and a few beaver on a small tributary. Waterfowl are especially common during the spring and fall migrations and include mallards, blue- winged teal, coots, wood ducks and Canada geese. Being located in a state park a large campground adjoins it and a guarded swimming beach has been provided. There is launching site for trailered boats with a large parking lot. In general access appears to be adequate for this body of water. Motor boating is prohibited.

Surface Acres = 96.0, S.D.F. = 2.4, Maximum Depth = 29 feet

Date  1968

Author   Surface Water Inventory Of Wisconsin

Cox Hollow Lake, Mill and Blue Mounds Creek Watershed (LW15) Fish and Aquatic LifeCox Hollow Lake, Mill and Blue Mounds Creek Watershed (LW15) RecreationCox Hollow Lake, Mill and Blue Mounds Creek Watershed (LW15) Fish Consumption

General Condition

Governor Dodge State Park Cox Hollow Beach was assessed for the 2018 listing cycle; E. coli data sample data were clearly below the 2018 WisCALM listing thresholds for the Recreation use. This beach was meeting this designated use and was not considered impaired.

Date  2017

Author  Ashley Beranek

Impaired Waters

Cox Hollow Lake (WBIC 1246500) was placed on the impaired waters list for excess algal growth in 2016. The 2018 assessments showed continued excess algal growth; new chlorophyll-a sample data exceeded the 2018 WisCALM listing thresholds for the Recreation use. Total phosphorus data were clearly below the Recreation use and Fish and Aquatic Life use listing thresholds. Based on the most updated information, no change in the existing impaired waters listing was needed.

Date  2017

Author  Ashley Beranek

Impaired Waters

Cox Hollow Lake (WBIC 1246500) was assessed during the 2016 listing cycle; chlorophyll sample data exceed 2016 WisCALM listing thresholds for the Recreation use, however, total phosphorus data do not exceed REC thresholds. Total phosphorus and chlorophyll data do not exceed Fish and Aquatic Life thresholds.

Date  2015

Author  Aaron Larson


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

Cox Hollow Lake is located in the Mill and Blue Mounds Creek watershed which is 186.74 miĀ². Land use in the watershed is primarily forest (54.60%), grassland (20.40%) and a mix of agricultural (15.30%) and other uses (9.80%). This watershed has 382.87 stream miles, 106.91 lake acres and 6,596.99 wetland acres.

Nonpoint Source Characteristics

This watershed is ranked Medium for runoff impacts on streams, Low for runoff impacts on lakes and High for runoff impacts on groundwater and therefore has an overall rank of High. This value can be used in ranking the watershed or individual waterbodies for grant funding under state and county programs.However, all waters are affected by diffuse pollutant sources regardless of initial water quality. Applications for specific runoff projects under state or county grant programs may be pursued. For more information, go to surface water program grants.

Natural Community

Cox Hollow Beach - Gov Dodge SP, Cox Hollow Lake is considered a Reservoir 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.