Waukesha County, Wisconsin
UR09
849600
795.30
Condition has improved over time; water is not impaired.
Notes
Oconomowoc Lake was placed on the impaired waters list due to mercury in fish tissue from 1998 to 2020. Samples showed this lake is covered by the general mercury fish consumption advisory. This lake was evaluated for phosphorus and algae every two years between 2012 and 2024 and these showed a healthy system. Aquatic plant communities were evaluated and were in good condition. This lake is on the Waters Attaining Standards List.Pollutant
Mercury
Listed For
Impairments
NA
Current Use
Listing Status
Water Delisted
Attainable Use
Priority
Delisted 2020
Designated Use
303(d) ID
326
Listing Date
4/1/1998
Impaired Water Notes
This listing was part of a set removed from the impaired waters list due to a change in fish consumption advisory levels in 2001. In 2001 Wisconsin DNR put into effect a statewide fish consumption advisory for mercury due to atmospheric deposition. Most of the lakes removed from the specific fish consumption advisories list in 2001 were not removed from the impaired waters list even though the thresholds had changed. For the 2020 assessment process WDNR requested delisting of 91 waters with residual mercury listings from prior to 2001. This request was approved by US EPA.
Date
9/4/2018