Halfmoon Lake, Muddy and Elk Creeks Watershed (LC13)
Halfmoon Lake, Muddy and Elk Creeks Watershed (LC13)
Half Moon Lake (2125400)
135.14 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 Seepage
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 lake is impaired
Total Phosphorus
Eau Claire
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 Seepage
Shallow seepage 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.
Streams capable of supporting a warm waterdependent sport fishery. Representative aquatic life communities associated with these waters generally require cool or warm temperatures and concentrations of dissolved oxygen that do not drop below 5 mg/L.
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.


Because of its shallow depth, enriched sediments and excessive water column phosphorus levels,
the lake experiences heavy macrophyte growth and severe algae blooms during the summer.
These eutrophic conditions have significantly impaired body contact recreational activities.
Historically, the lake frequently experienced winterkill conditions, but since the City installed
aerators in 1979, adequate dissolved oxygen conditions have been maintained throughout the
Algae blooms in Half Moon Lake are often accompanied by excursions of the Wisconsin water
quality criterion for pH. The elevated lake pH levels are due to removal of carbon dioxide from
water during photosynthesis (by macrophytes and algae). The reduction in carbon dioxide levels
during daylight causes an increase in pH. A reduction in phosphorus levels would result in a
decrease in chlorophyll levels (a measure of productivity) and a reduction in maximum pH levels.
The lake was placed on the Wisconsin 303(d) list in 1998 and 2002 due to eutrophication and pH
exceedances above the 9.0 water quality standard. Lake sampling conducted by the Wisconsin
Department of Natural Resources (WDNR) during the summers of 1997 and 2001 found pH
levels above 9.0 on 4 of 4 (100%) of the summer sample dates when all sites are considered. In
addition, bi-weekly monitoring conducted by the U.S. Corps of Engineers (USCOE) during
summer 1999 found pH violations on 8 of 11 dates (73%).
In 2001, a Half Moon Lake Advisory Task Force was appointed by the Eau Claire City Council to
prepare a report and recommendations to improve water quality in Half Moon Lake. The task
force (which was advised by WDNR staff) developed recommendations that form the basis of this

During summer 1999, the USCOE conducted a study to examine nutrient
loadings from storm sewer inflows, profundal sediments, decaying macrophytes, and motor boat
activity (James et. al., 2001). Water samples were collected from storm sewers and the outlet
structure of Half Moon Lake to determine external loadings and discharges.
External sources of phosphorus include storm sewer discharges, precipitation, direct drainage and
groundwater pumped into the lake from the Owen Park wells. These sources represent 21 percent
of the seasonal phosphorus load to the lake

Half Moon Lake is included on the Wisconsin Department of Natural Resources (WDNR) 1998
and 2002 303(d) list of impaired waters. The lake is listed as a high priority waterbody and is
impaired as a result of phosphorus from urban runoff and internal loading. The external load is
nonpoint source dominated, with no industrial or municipal wastewater treatment plant discharges
to the lake.

Half Moon Lake is currently not meeting applicable narrative water quality criterion as defined in
NR 102.04 (1); Wis. Admin. Code. WWSF, and for pH criterion exceedences-- no change greater than 0.5 units
outside the estimated natural seasonal maximum and minimum.
Documented water quality standard pH violations were a primary reason for including Half Moon
Lake on the 303d list. However, we found no clear relationship between pH and chlorophyll
and/or phosphorus in Half Moon Lake. The pH exceedances may be more related to macrophyte
photosynthesis and low buffering capacity than algal productivity. For this reason, goals
established by this TMDL were not based on the pH criterion, but rather chlorophyll-a and
phosphorus levels. Generally, reductions in phosphorus and chlorophyll-a levels should result in
decreased pH levels.
Although Half Moon Lake is also on the 303d list for impairment caused by sedimentation, the
sources of sediment to the lake have generally been controlled. Most of the inorganic sediment
sources were short term and related to construction erosion in the watershed. Historical organic
sedimentation from the logging era is a continuing source of phosphorus release.

Date  2006

Author   Aquatic Biologist


Half Moon Lake (Hydrologic Unit Code 070500006) is a small, shallow eutrophic lake that
formed as an oxbow of the Chippewa River. The lake is geographically located within the City of
Eau Claire and the Lower Chippewa River Basin. The lake is highly eutrophic and exhibits
excessive algae and aquatic macrophyte growth (Borman, 1990; Brakke, 1995; Konkel and
Borman, 1996; James et. al., 2001, 2002). Half Moon Lake was originally listed on Wisconsin’s
303(d) impaired waters list in 1998 for eutrophic conditions and sedimentation and listed as a
high priority for TMDL development on the October 2002 303(d) list.
Half Moon Lake is 53 hectares (132 acres) in size with a maximum depth of about 3 meters
(slightly over 9 feet). The lake’s watershed is 577 acres and approximately 85% of the shoreline
is publicly owned by the City of Eau Claire. Land use in the watershed is 45% residential, 41%
open land and 14% commercial (Barr Engineering, 1992). The City has a policy of purchasing
properties abutting the lake when they become available and at the present time, only four
privately owned properties remain along the shoreline.
During initial settlement of the City of Eau Claire, Half Moon Lake played an important role as a
reservoir for logging operations during the late 1800’s. Several sawmills were located on the lake
and various channels connected the lake to the Chippewa River. These connections between the
lake and river eventually filled in and water levels are now maintained by seepage, stormwater
runoff and groundwater pumping from shallow wells. The pumping facilities consist of three
shallow wells located near the edge of the Chippewa River with each pump rated at one million
gallons per day. The pumps provide make-up water to the lake and operate year round on a
rotating basis with two pumps running simultaneously at all times.
Some of the watershed drainage has been routed away from the lake, and the entire hydrologic
system has been altered (Brakke, 1995). Use of the lake for log storage during the mid-1800s may
explain the high organic content of its sediments (tree bark and sawdust), that also contribute to
lake nutrient levels (Barr Engineering, 1992).
Since the early 1970s, many changes have occurred within the lake and its watershed, including:
· diversion of a significant portion of the storm sewer watershed to the Chippewa River,
· construction of an earthen dike to prevent inflow to the lake from Sherman Creek,
· construction of a new outlet structure on the southwest end of the lake,
· and, installation of wells and pumps in Owen Park along the Chippewa River to provide
make-up water to the lake
The lake is used extensively for recreation, especially boating and fishing. Although boating is
allowed on the lake, no outboard motors are allowed with the exception of the Ski Sprites, a local
water-ski club that uses the lake for practice and exhibition shows during the summer. The Ski
Sprites use ski boats with high horsepower outboard motors for these activities.

Date  2006

Author   Aquatic Biologist


Half Moon Lake is an oxbow lake near the Chippewa River in the city of Eau Claire. The lake is a
major recreational resource that surrounds Carson Park, which draws several thousand visitors
annually. The lake has a long history of water quality degradation and lake restoration activities.
The lake was the site of several sawmills from 1860 until 1920. These mills deposited bark, sawdust
and runoff from manure piles into the lake. The lake experienced prolific growths of plants and
algae during this period. The lake likely received raw domestic waste from riparian dwellings until
1940 when sanitary sewers were installed in the city. The lake was historically treated with aquatic
herbicides from the 1940s until 1989.
The first lake restoration attempt, aimed at alleviating nuisance plants and algae growth, was the
diversion of Sherman Creek in 1959. A major lake restoration effort was conducted in the late
1970s and early 1980s that included diversion of storm water, use of groundwater to maintain lake
levels, construction of an overflow structure, winter aeration, limited dredging, rough fish removal,
and the application of aquatic herbicides. The completion of this lake restoration effort did not
alleviate the nuisance plants and algae growth or low winter dissolved oxygen concentrations.
The Half Moon Lake Advisory Committee was formed in the late 1980s for the improvement of
water quality in Half Moon Lake. This committee agreed that the lake should be managed primarily
for fishing, non-motorized surface use, and aesthetic beauty. The city has begun to implement
several management activities to achieve these primary uses.

Date  1996

Author   Aquatic Biologist


The city purchased an aquatic plant harvester, and since 1991 has been implementing an aquatic
plant harvesting program developed by the city and WDNR. The objectives of the harvesting
program have been to alleviate nuisance aquatic plant growth and improve boating access and fish
habitat. To date, the harvesting program appears to be meeting all of the objectives (Borman).
The city obtained a Fish America Foundation grant in 1992 to purchase and install a new winter
aeration system for the lake. Weekly dissolved oxygen monitoring during winter 1992-93 and 1993-
94 indicated that the aeration system is able to maintain minimum dissolved oxygen concentrations
near 5 milligrams per liter (mg/l) throughout most of the lake. It is critical to maintain levels near 5
mg/l to maintain a walleye fishery.
The city obtained a grant from WDNR to assess phosphorus contributed by the lake's watershed
and the management options for controlling it. This study concluded that internal phosphorus
cycling was a major source of phosphorus, stimulating nuisance aquatic plant and algae growth. The
study recommended control of phosphorus inputs from the watershed and defining the source of
internal phosphorus loading.
The city received a lakes planning grant for assessing the source of internal phosphorus loading.
This assessment was conducted by the University of Wisconsin-Eau Claire during 1994. Ths study
was designed to determine if Half Moon Lake develops an anoxic layer at the sedimendwater
interface during the summer, and if the operation of hlgh powered motor boats by the S h Sprites
water skiing club harms water quality.
The study found that Half Moon Lake does intermittently stratify for short periods during the
summer. During periods of stratification, dissolved oxygen levels become depressed in the bottom
meter of the lake, allowing phosphorus to be released from the sediment. The study also determined
that use of Half Moon Lake for the local water ski show affects the lake. The use of high power
motors on the lake mixes the lake top to bottom in the area used for the ski show. The report
documented hgh total phosphorus levels in the portion of the lake used for the ski show during
the study period. It appears the ski show does have an impact on lake water quality, but the
significance of the impact was not determined (Bradte).

Date  1996

Author   Aquatic Biologist

Historical Description

Source: 1964, Surface Water Resources of Eau Claire County Halfmoon Lake, T27N, R9W, Section 19

A soft water, seepage lake within the City of Eau Claire. Part of the flow of Sherman Creek is diverted to the lake by a 3- foot water control and diversion structure. It is an oxbow lake located in an old meander channel of the Chippewa River. It was chemically rehabilitated in 1958 to remove an abundant carp and buffalo population. The present fish include northern pike, largemouth bass and bluegills. An abundance of buffalo, however, is still a problem. The lake also has a serious algae problem and an intensive algae control program is carried out on the lake annually. The east shore of the lake is in the residential section of the city, and the central island portion is a recreation area, Carson Park, where swimming, picnicking and public access facilities are provided. The Eau Claire Rod and Gun Club Park on the west shore provides picnicking facilities. Another swimming beach on the north shore off Grand Avenue. Three acres of wetlands in the southwest bay provide nesting habitat for puddle ducks--mainly, occasionally, Canada geese use the lake during migratory seasons. A local boating regulation prohibits water skiing.

Surface Acres = 134.0, S.D.F. = 3.05, Maximum Depth = 12 feet

Date  1964

Author   Surface Water Inventory Of Wisconsin

Halfmoon Lake, Muddy and Elk Creeks Watershed (LC13) Fish and Aquatic LifeHalfmoon Lake, Muddy and Elk Creeks Watershed (LC13) RecreationHalfmoon Lake, Muddy and Elk Creeks Watershed (LC13) Fish Consumption


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 Implementation Initiated
The City of Eau Claire is sponsoring a Lake Management Planning Implementation project aimed to control internal sediment phosphorus loading in Halfmoon Lake by applying alum. The lake received an initial AL treatment in 2011 and was effective at maintaining TP WQ goals for three years, however after five years the effects have diminished. The initial alum treatment dosage was adequate however the floc did not sink into the upper sediment due to higher bulk density characteristics allowing upward P diffusion and decreasing binding efficiency of phosphorus.
ATTAINS Implementation Initiated
The City of Eau Claire proposes to apply aluminum sulfate-sodium aluminate to the sediments of Half-Moon Lake in Eau Claire County to reduce phosphorus inputs from this source. Major project elements to include: 1) Alum treatment, and 2) Limnilogical monitoring.
ATTAINS Implementation Initiated
The City of Eau Claire proposes to design detention ponds that will hold storm drainage from the roof of the school and hard surfaces around the school for lake protection.
ATTAINS Implementation Initiated
The City of Eau Claire will acquire two city lots and will be used for lake protection purposes. The land will contain an undisturbed vegetative buffer of at least 30 foot along the lakeshore. Mowed blue grass to the water's edge isn't permitted. A trail will be developed for pedestrians and bicycles to connect to the existing trail system within Carson Park.
TMDL Implementation
Halfmoon Lake was originally listed on Wisconsin's 303(d) impaired waters list in 1998 for eutrophic conditions and sedimentation and listed as a high priority for TMDL development on the October 2002 303(d) list. Halfmoon Lake is 53 hectares (132 acres) in size with a maximum depth of about 3 meters (slightly over 9 feet). Implementation Plan is needed.
TMDL (USEPA) Approved
Half Moon Lake was originally listed on Wisconsin's 303(d) impaired waters list in 1998 for eutrophic conditions and sedimentation and listed as a high priority for TMDL development on the October 2002 303(d) list. Half Moon Lake is 53 hectares (132 acres) in size with a maximum depth of about 3 meters (slightly over 9 feet).

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

Halfmoon Lake is located in the Muddy and Elk Creeks watershed which is 237.94 miĀ². Land use in the watershed is primarily agricultural (48.60%), forest (21.80%) and a mix of grassland (16.80%) and other uses (12.80%). This watershed has 313.30 stream miles, 590.92 lake acres and 11,999.60 wetland acres.

Nonpoint Source Characteristics

This watershed is ranked Medium for runoff impacts on streams, High 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.This water is ranked High Lake for individual Lakes based on runoff problems and the likelihood of success from project implementation.

Natural Community

Half Moon Lake is considered a Shallow Seepage 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 seepage lake describes the depth and location of the lake in a watershed. These variables affect the lakes response to watershed variables.

Fish Stocking