West branch Sugar River and Mount Vernon Creek watershed (SP16)

The west branch Sugar River and Mount Vernon Creek watershed is located in southwestern Dane County. The watershed is dominated by agricultural land uses.

The Mount Horeb wastewater treatment plant is the only permitted facility discharging effluent to surface waters in the watershed. Mount Horeb is a "bedroom community" in the Madison metropolitan area. It will likely continue to experience significant population growth over the next 10 years, affecting the life of the present wastewater treatment plant. This growth may also degrade water quality and in-stream habitat in the upper reaches of the west branch Sugar River and Deer Creek.

The community of Mount Vernon is an unsewered residential area in the watershed. Failing septic systems in Mount Vernon may be degrading water quality in this reach of the stream. Part of the watershed was in a U.S. Soil Conservation Service P.L. 566 watershed plan, which began in 1981. The goals of the plan were to provide watershed protection, improve water quality and enhance fish and wildlife habitat (Dane County, 1981-8). A 1990 evaluation of the project stated the project "partially achieved its purpose" (Barthel, 1990).

Deer Creek

Deer Creek rises on the southeast edge of Mount Horeb and flows southeast, joining with Fryes Feeder to become Mount Vernon Creek. Its current use classification is for support of a warmwater forage fishery, although it could potentially support a trout fishery (Wisconsin DNR, 1992¹). Brown and Brook trout have been found in Deer Creek (Wisconsin DNR, 1993²).

This stream was part of the P.L. 566 project area. Water quality problems identified included runoff from barnyards and cultivated fields and excessive grazing. Habitat improvement projects occurred at sites along the stream, which helped the trout fishery in the stream. Biotic index monitoring in 1990 did not, however, demonstrate water quality improvements (Wisconsin DNR, 1992¹). One "bad actor" along the stream may have offset all the improvements made in the Deer Creek sub-watershed.

This is Deer Creek in the west branch Sugar River watershed near Mt. Horeb. Deer Creek is ERW coldwater stream. The section shown is one where the stream has been narrowed, banks stabilized and fish habitat structures installed this summer and fall. The work was done using state and local funding as a Targeted Runoff Management (TRM) project. The Upper Sugar River watershed Initiative also had a role in getting this project off the ground.

Increased residential development is occurring along Deer Creek. Such development may have a long-term cumulative impact on water quality and fishery of the creek. Improved water quality and in-stream habitat in Deer Creek are vital to the protection of Mount Vernon Creek. Redside dace, a watch species fish, is found in the stream (Fago, 1982). Deer Creek is an Exceptional Resource Water stream under the state's anti-degradation rules.

Flynn Creek

Flynn Creek is a tributary to the west branch Sugar River. Approximately 2.5 miles of it is classified as class II trout waters (Wisconsin DNR, 1980). Biotic index data collected in 1986 and 1987 showed water quality ranging from very good to fairly poor. Stream habitat rated fair. Runoff from croplands and pastures causes siltation in the stream. Redside dace, a watch species fish, occur in the stream (Fago, 1982). Flynn Creek is an Exceptional Resource Water stream under the state's antidegradation rules.

Fryes Feeder

Fryes Feeder joins with Deer Creek to form Mount Vernon Creek. About 1.5 miles of its length is classified as a class II trout stream (Wisconsin DNR, 1980). Biotic index data from May of 1990 indicates the stream has very good water quality (Barthel, 1990). Fryes Feeder is an Exceptional Resource Water stream under the state's anti-degradation rules.

Milum Creek

Milum Creek is a small tributary to the west branch Sugar River. Its current use classification indicates it supports a warmwater forage fishery, but it could potentially support a coldwater sport fishery. Data from 1986 and 1987 indicate poor in-stream habitat, but water quality ranged from good to very good (Marshall, 1988⁴). Siltation from cropland erosion seems to be the primary problem limiting water quality. Redside dace, a watch species fish, are found in the stream (Fago, 1982). Milum Creek is an Exceptional Resource Water stream under the state's anti-degradation rules.

Mount Vernon Creek

Mount Vernon Creek is classified as a trout stream for its entire length. About four of its almost eight miles are class I trout waters, with the remainder rated class II (Wisconsin DNR, 1980). The class I portion of the stream has been elevated to outstanding resource water (ORW) status, providing it with a higher level of protection.

The remainder of the stream is classified as Exceptional Resource Waters under the state's anti-degradation rules. Sources of polluted runoff threaten parts of this stream, but the total extent of the threat has not been evaluated. Increased nitrate concentrations have been documented, apparently directly related to agricultural changes in the watershed (Mason et.al., 1990). The unincorporated community of Mount Vernon is located on the class I portion of the creek. The community uses individual septic systems to handle its wastewater. Many of these systems are suspected of failing and may be degrading water quality in Mount Vernon Creek.