McMahon Lake

McMahon Lake Quick Facts

  • DNR Lake ID Number:  70-005000
  • Surface Area:  162.26 acres
  • Littoral Area:  157.93 acres
  • Lake Watershed Area:  393 acres
  • Maximum Depth: 14 feet
  • Mean Depth:  8.5 feet
  • Ordinary High Water Level:  965.2 feet above sea level
  • Public Boat Access:  One DNR public access is available off Mushtown Rd/C.R. 87
  • Water Quality Impairment Status:  Impaired for nutrients and mercury. The completed nutrient TMDL can be reviewed here.
  • High water no wake restrictions:  When the lake level exceeds 965.2 feet NVGD 29

Water Quality

McMahon Lake was removed from the Federal Impaired Waters List (303d List) in 2018 due to improvements in water quality.  State standards for shallow lakes in the North Central Hardwood Forest (NCHF) region for the three lake parameters we track are provided in the following table. If a parameter meets for falls below that standard unit, that parameter is meeting water quality standards. 

State Standards for Shallow Lakes in the North Central Hardwood Forest Ecoregion


Standard (units)

Total Phosphorus

60 μg/L


20 μg/L

Secchi Disk Transparency

Greater than 1m

Additional water quality reports and information can be found in Annual Reports.

Water Quality 2005-2021


Invasive Species

McMahon lake currently as two aquatic invasive species, Curlyleaf pondweed and Eurasian watermilfoil.  The Scott WMO treats the public access bay for curlyleaf pondweed each year as a preventive measure of spreading it to other lakes.

Curly leaf

Lake Vegetation Surveys

2007, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021

McMahon Lake June 16, 2020

McMahon Lake June 15 2020

McMahon Lake May 2022

McMahon Lake May 2022 - Zebra mussel

Studies Specific to McMahon Lake

McMahon Lake Improvement District

McMahon Lake Improvement District (MLID) is a political subdivision of the State of Minnesota and was established by the Scott County Board of Commissioners on March 15, 2022.