Dane County, Wisconsin
LR09, LR10
805400
9,780.93
Water is impaired due to one or more pollutants and associated quality impacts.
Notes
Lake Mendota was evaluated for phosphorus and algae every two-year cycle between 2012 and 2024. Phosphorus levels were found to be too high, which was reflected in algal blooms. The TMDL restoration plan was approved in 2011. There is an ongoing Clean Yahara Project to address nutrient loadings to this lake. Water column and fish tissue PFOS sampling in 2020 and 2022 showed no elevated levels.Pollutant
Total Phosphorus
Listed For
Recreation
Impairments
High Phosphorus Levels, Excess Algal Growth
Current Use
Restricted Recreation
Listing Status
TMDL Approved
Attainable Use
Recreation
Priority
Not Applicable
Designated Use
Recreation
303(d) ID
2012-2027
Listing Date
4/1/2012
Impaired Water Notes
This water was assessed during the 2018 listing cycle; total phosphorus sample data overwhelmingly exceeded 2018 WisCALM listing thresholds for the Recreation use and Fish and Aquatic Life use.
Date
7/11/2017
Impaired Water Notes
Lake Mendota data summary --- Total phosphorus (TP) and chlorophyll a (chl. a) data collected at the deep hole location by WDNR and/or UW's Long Term Ecological Research (LTER) program exceed the TP recreational impairment threshold and the chl. a recreational impairment threshold (Mendota attachment). Additionally, Dane County, which manages Lake Mendota?s eight public beaches, reported 58 beach closures from 2007-2010 on Lake Mendota due to blue-green algae blooms, leading to 182 lost beach days (Beach closure attachment). Dane County also collected 43 cyanotoxin samples at Lake Mendota beaches during algal blooms and 23 of these samples exceed the World Health Organization's (WHO) high risk threshold for exposure to cyanotoxins. The WDNR also collected three chl. a samples from Lake Mendota beaches in 2004 and 2005 and two of these samples exceeded the WHO's high risk threshold for exposure to cyanotoxins (Mendota attachment)
Date
11/18/2013
Impaired Water Notes
This water was assessed during the 2014 listing cycle; total phosphorus sample data overwhelmingly exceed 2014 WisCALM listing thresholds for the Recreation use and Fish and Aquatic Life use.
Date
2/28/2014
Impaired Water Notes
This water was assessed during the 2016 listing cycle; total phosphorus sample data overwhelmingly exceed 2016 WisCALM listing thresholds for the Recreation use and Fish and Aquatic Life use.
Date
10/19/2015
Impaired Water Notes
This water was assessed during the 2020 listing cycle; new total phosphorus sample data overwhelmingly exceeded 2020 WisCALM listing thresholds for the Recreation use and Aquatic Life use. Based on the most updated information, no change in existing impaired waters listing is needed.
Date
8/2/2019
Pollutant
PCBs
Listed For
Impairments
NA
Current Use
Listing Status
Pollutant Removed
Attainable Use
Priority
Delisted 2022
Designated Use
303(d) ID
280
Listing Date
4/1/1998
Impaired Water Notes
New fish tissue samples resulted in the removal of site specific fish consumption advice for PBCs in Lake Mendota.
Date
1/22/2021