Onion River, Mullet River,Onion River,Sheboygan River Watershed (SH03, SH04, SH05)
Onion River, Mullet River,Onion River,Sheboygan River Watershed (SH03, SH04, SH05)
Onion River (51200)
31.80 Miles
0 - 31.80
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.
Cool-Cold Mainstem, Cool-Warm Mainstem
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.
This river is impaired
Degraded Biological Community
Total Phosphorus
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.
Fish and Aquatic Life - waters that do not have a specific use designation subcategory assigned but which are considered fishable, swimmable waters.
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.


T15N R22E Sec. 36 NESE **9** Stream Length = 44.0 miles **9**
The Onion River discussion is segmented into two sections to represent the different stream classifications and biological characteristics of the stream from its headwaters downstream. The Onion River is classified as a Cold Water Fish Community stream, Class II trout stream from the headwaters downstream to the top of the Waldo Dam impoundment. A Warm Water Sport Fish Community classification exists from the Waldo Impoundment downstream to the confluence with the Sheboygan River.

The lower Onion River extends from the Waldo Dam downstream to its confluence with the Sheboygan River at Rochester Park. It does not completely achieve its potential to support a warm water sport fish community because of water quality and habitat limitations. The reach flows through vast acreage of farmland, where intensive pasturing contributes to erosion and sedimentation. Even light rains, or during periods when the carp are active, the stream becomes turbid, resulting in heavy siltation, and increased nutrient levels due principally to agricultural pollutants (pers. comm. Galarneau). The lower Onion River supports a tolerant warm water fishery with carp, bullhead, northern pike, and green sunfish present.

Overall the Onion River water quality has changed little from the information presented in the Onion River Priority Watershed Plan (WDNR 1981) as compared to our monitoring in 1994. Water quality is still good to excellent in the rivers upstream reaches (above Waldo) and poor in the river’s lower reaches. The rivers tributary streams, specifically Belgium Creek and Lima tributary, are severely degraded due to both point and nonpoint sources and ultimately effect the water quality in the Onion River.

The Onion River Priority Watershed Plan (WDNR 1981) reported that both the biotic index samples and the water chemistry samples above the Hingham impoundment were indicative of good to excellent water quality. While samples collected at the downstream end of the watershed (Ourtown Road) rated the river's water quality as poor. Similar results were observed from our 1994 Onion River water quality monitoring (WDNR 1999).

WDNR personnel surveyed the Onion River approximately 1.6 miles downstream of Ourtown Road in July 2000 (River mile 2.8). The stream reach that was surveyed was within the boundaries of the Pinehurst (“The Bull”) Golf Course. The fish community rated good and included the following species: sand shiner, common shiner, white sucker, greater redhorse, longnose dace, hornyhead chub, smallmouth bass, bluntnose minnow, rock bass, common carp, green sunfish, bigmouth shiner, johnny darter, northern pike, stonecat, blackside darter, black bullhead, black crappie, and bluegill. Stream habitat consisted of a good variety of bottom substrates and habitat types. There were numerous riffle, pool and run areas within the sample reach. However, fish cover was fairly limited. Vegetated buffer areas were good within the stream reach, but heavy agricultural land use within the watershed does contribute a large portion of the sediment and nutrient loading to the Onion River. Future monitoring will be done to determine if the new golf course will have an impact on the stream ecosystem.

This segment of the Onion River extends form the headwaters downstream to the top of the pool formed by the Waldo Dam. The potential fishery is currently limited by increased water temperature due to the impoundment and presence of private fish ponds on major spring sources, and siltation from agricultural runoff. This segment is classified as a cold water fish community, Class II trout stream but has the potential of being a Class I stream. The headwaters, Ben Nutt Creek maintains a good diversity of intolerant fish species with tolerant and very tolerant fish species present. Intolerant species include brook and brown trout. Tolerant and very tolerant species include green sunfish, stonecat, and carp.

The diversity of macroinvertebrates is only moderate and decreases in the downstream reaches of this segment. Tolerant stream bottom insects dominate, but the HBI falls in the range of "excellent" to "fair" water quality. This segment supports the most balanced fish and aquatic life community in the watershed.

WDNR personnel surveyed the Onion River upstream of County Highway U in July 2000. The survey was conducted upstream and downstream of a large dairy farm operation for a total of two sample sites. This was done to collect baseline data for a future stream relocation project that is designed to reduce nonpoint source pollutant loading to the stream and improve the stream ecosystem. Downstream areas did appear to be impacted from the farm runoff when compared to the upstream site.

Downstream of the dairy farm the fish community rated poor. Fish species included white sucker, mottled sculpin, brown trout, creek chub, northern brook lamprey, rainbow trout, brook stickleback, common carp, brook trout, central mudminnow, and golden shiner. Stream habitat was impacted by the dairy farm with inadequate buffer areas along the streambank, sedimentation on the bottom substrate, bank erosion, and lack of fish cover.

Upstream of the dairy farm the fish community rated fair. Fish species included brown trout, mottled sculpin, white sucker, northern brook lamprey, and rainbow trout. Stream habitat had an excellent buffer of woodland, shading was higher, bank erosion was minimal, bottom substrate had more rock and gravel, and fish cover was better, but still limited.

Date  2001

Author   Aquatic Biologist

Historical Description

BEN NUTT CREEK T15N R21E Sec. 30 **9** Stream length = 6.0 miles

As the major headwater tributary to the Onion River, this creek drains an area of about nine square miles in the southwest corner of the town of Plymouth. Although classified as a Class II trout stream, brown trout reproduction has been reduced by the presence of dams, ponds, and raceways that cause temperature fluctuations in the headwater springs. Brown trout are planted annually, and the stream experiences heavy fishing pressure. The Hilsenhoff biotic index (HBI) value for the creek was 5.88 indicating "fair" water quality (WDNR 1991). The fishery is composed of brown trout, bluntnose minnow, blacknose dace, creek chub, pearl dace, white sucker, brook stickleback, johnny darter, and mottled sculpin.

Date  2001

Author   Surface Water Inventory Of Wisconsin

Onion River, Mullet River,Onion River,Sheboygan River Watershed (SH03, SH04, SH05) Fish and Aquatic LifeOnion River, Mullet River,Onion River,Sheboygan River Watershed (SH03, SH04, SH05) RecreationOnion River, Mullet River,Onion River,Sheboygan River Watershed (SH03, SH04, SH05) Fish Consumption

General Condition

The Onion River (also known as Ben Nutt Creek) was assessed during the 2018 listing cycle; new biological (macroinvertebrate Index of Biotic Integrity (IBI) scores) sample data were clearly below the 2018 WisCALM listing thresholds for the Fish and Aquatic Life use. This water was meeting this designated use and was not considered impaired.

Date  2017

Author  Ashley Beranek

General Condition

Onion River (51200) from Cth N to its headwaters was assessed during the 2016 listing cycle; total phosphorus and biological (macroinvertebrate and fish Index of Biotic Integrity (IBI) scores) sample data were clearly below 2016 WisCALM listing thresholds for the Fish and Aquatic Life use. This water is meeting this designated use and is not considered impaired.

Date  2015

Author  Ashley Beranek

Impaired Waters

The Onion River (51200), from its mouth to Cth N, was added to the impaired waters list for total phosphorus in 2012. The 2016 assessments showed continued impairment by phosphorus; total phosphorus sample data exceed 2016 WisCALM listing criteria for the Fish and Aquatic Life use and biological impairment was observed (i.e. at least one macroinvertebrate or fish Index of Biotic Integrity (IBI) scored in the poor condition category). Based on the most updated information, no change in existing impaired waters listing is needed.

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.



ATTAINS Alternative Restoration Approach
This grant is to conduct a river restoration project on the Onion River in Sheboygan County, Wisconsin. The goal of the Onion River restoration project is to return the stream to its previous condition as a blue ribbon trout stream with a substantial and self-sustaining population of wild trout. This grant will be used for the improvement and restoration of the Onion River from County Highway "U" and continue upstream to County Highway "E". A final report shall be made to the WDNR on all activities performed and completed for this grant agreement. Work will be documented in written and photographic form. Amended scope Jan. 11, 2005 - Expand restoration footage from 2000 to 4000 feet. The work includes improving stream flow through narrowing and deepening, placement of lunkers for bank stabilization & trout habitat and placement of rock instream for habitat & food growth.
ATTAINS Water Identified for Protection
The Lakeshore Chapter of Trout Unlimited overall goal of the Onion river Project is to return the Onion River to the high quality trout stream it once was, establishing a self-sustaining wild trout population through the improvement of water quality, flow, and trout habitat. The 3 ways of improvement are: 1) Recreate and improve spawning grounds for trout, 2) Remove barriers to the upstream passage of spawning grounds, 3) Reroute stream away from an existing cowyard to reduce runoff. Intent of this project is to use data collected from this research to guide future project planning.
Nine Key Element Plan
Onion River PWS Plan - Nine Key Element Plan - The Onion River Priority Watershed Project plan assesses the nonpoint sources of pollution in the Onion River Watershed and guides the implementation of nonpoint source control measures. These control measures are needed to meet specific water resource objectives for the Onion River and its tributaries. The purpose of this project is to reduce the amount of pollutants originating from nonpoint sources that reach surface water and groundwater within the Onion River Priority Watershed Project area.

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

Onion River is located in the Sheboygan River watershed which is 260.12 miĀ². Land use in the watershed is primarily agricultural (47.30%), grassland (17.60%) and a mix of wetland (16.70%) and other uses (18.30%). This watershed has 340.24 stream miles, 4,345.33 lake acres and 27,968.05 wetland acres.

Nonpoint Source Characteristics

This watershed is ranked Not Available for runoff impacts on streams, Not Available 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

Onion River is considered a Cool-Cold Mainstem, Cool-Warm Mainstem 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.

Cool (Cold-Transition) Mainstem streams are moderate-to-large but still wadeable perennial streams with cold to cool summer temperatures. Coldwater fishes are common to uncommon, transitional fishes are abundant to common, and warm water fishes are uncommon to absent. Headwater species are common to absent, mainstem species are abundant to common, and river species are common to absent.

Fish Stocking
Fish Species

The purpose of the trout survey of the upper Onion River Watershed in 2004 was twofold. The first objective was to monitor changes in the brown trout population of the Onion River in relation to habitat improvements and wild trout stocking. The second objective was to determine the effect of a change in fishing regulations upstream (west) of CTH “E” (Figure 1).
Habitat improvement projects have been ongoing in the upper watershed in recent years. During the summer of 2004, habitat work was done on the Drewry farm immediately downstream of CTH “E” (Station 2, Figure 1). In 2003, habitat work was done between Winooski Road and CTH “U” (Station 1). Work was also done in 2004 on the Laack parcel upstream of CTH “E” (Station 3), and on the Bohnhoff farm upstream of Station 3.
A change in the trout fishing regulations took effect with the start of the general fishing season in 2004. The Onion River upstream of CTH “E”, Mill Creek, Ben Nutt Creek, and their tributaries were regulated by a 15” minimum size, one daily bag limit and artificial lures only restrictions. Stations 3 through 8 were regulated by the more restrictive regulations.
Wild brown trout fingerling were stocked into the watershed in 1997, 1999 and 2000. 1,150 adult and juvenile brown trout were stocked into the Onion River in October, 1997 from the Coon Valley area in southwestern Wisconsin. Another 891 adult and juvenile wild browns from Coon Valley were stocked again on October 6, 2003. All of the wild fish stocked into the stream were clipped with an adipose fin clip to distinguish them from naturally reproduced fish.

Date  2004

Author  John Nelson