Lake Monona

Lake Monona

Lake Monona is the second lake in the Yahara chain. The land surrounding the lake is mostly urban and is fed by the Yahara River, Wingra Creek, and Starkweather Creek. Over the years, Lake Monona has faced water quality issues from urban runoff and from industrial sites. Current point source discharges in the watershed include:
  • Dane Country Regional Airport and Madison-Kipp Corporation (to Starkweather Creek)
  • Madison Gas & Electric Company (to Lake Monona)
  • UW-Madison at Charter Street (to Lake Monona via storm sewers)
  • Wisconsin Department of Natural Resources’ Nevin Fish Hatchery (to Nine Springs Creek)
Besides the Yahara River, the largest source of phosphorus coming into Lake Monona is from Starkweather Creek. Most of the phosphorus entering the lake from the Monona watershed comes from urban sources. Leaf management and construction erosion presents significant opportunities for phosphorus reduction. Lake Monona map

Lake Monona by the numbers

Lake Mendota and Lake Monona together form Madison’s iconic isthmus, one of only two State capital cities in the nation to be located on an isthmus. It is the only other lake in the chain classified as “deep” by the Wisconsin Department of Natural Resources criteria.
  • Watershed area: 61,643 acres
  • Surface area: 3,274 acres
  • Shoreline: 13 miles
  • Maximum depth: 64 feet
  • Mean depth: 27 feet
  • Flushing rate: 1.3 years

Water clarity

  • 5.1 feet or “good” according to Department of Natural Resources criteria for deep lakes (2017)


  • Open 93% of the time and closed 7% of the time (2017)
  • 5 closure days due to E.coli bacteria; 27 closure days due to blue-green algae (2017)
  • 19 additional closure days at Olbrich Park due to both E.coli and blue-green algae (2017)

Olbrich Beach Lake Monona

Phosphorus levels

  • 0.037 mg/L or “fair” according to Department of Natural Resources criteria for deep lakes (2017)

The cities of Madison and Monona have invested in stormwater projects to reduce phosphorus runoff into the lake with grant support from Dane County. For an update on the latest phosphorus reduction projects within the watershed, see the State of the Lakes Annual Report.

Organizations supporting Lake Monona

The following groups work on water quality issues in the Lake Monona watershed. Consider contacting an organization near you to get involved and let us know if we have missed your group! City of Madison City of Monona Dane County Friends of Monona Bay Friends of Starkweather Creek Friends of the Yahara River Parkway Madison Water Utility Public Health Madison & Dane County Yahara Watershed Improvement Network