Lake Mendota
Lake Mendota in Dane County, Wisconsin has a water quality grade of D (Nutrient-rich). Water clarity: 5 ft visibility. Phosphorus: 65.4 µg/L. Maximum depth: 83 ft. Surface area: 9781 acres.
Wisconsin DNR rates Panfish as abundant on Lake Mendota. DNR survey details →
- Clarity
- 5 ft
- Max depth
- 83 ft
- Area
- 9,781 acres
- Type
- Eutrophic
- Trend
- ↓ Declining
- Public access
- Yes
Grade D measures nutrients and algae, not whether this is a good place for a cabin trip. Cabins and rentals near Lake Mendota →
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Lake Mendota is a 9,781-acre productive, nutrient-rich eutrophic lake in Dane County, Wisconsin with a maximum depth of 83 feet. Water quality is graded D based on 1 sampling years through 2026. Overall water quality is declining over recent sampling years. The lake supports 8 documented fish species including Musky, Panfish, and Largemouth Bass. Public access is available with 5 public boat landings and 7 public beaches. Compared to the 14 other monitored lakes in Dane County, Lake Mendota ranks #9 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-08. Grade methodology: LakeQuality methodology.
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Lake Mendota Water Quality Report Card (2026)
A printable one-page report card for Lake Mendota: grade, clarity, phosphorus, algae, multi-year trend, depth, and fish — with sources.
Swimming Safety
Grade onlyElevated nutrients
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum
Water Quality Grade: D (Nutrient-rich)
Murky, only visible to about 5 ft. Phosphorus level: 65.4 µg/L. Trophic State Index: 59.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5 ft | Not graded |
| Phosphorus | 65.4 µg/L | Poor |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 59 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Lake Mendota
Compare lakeside cabins, hotels, and vacation rentals near Lake Mendota in Dane County, Wisconsin — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Lake Mendota are listed below.
Top-rated places to stay near Lake Mendota
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip? Cabins and lodging at Lake Mendota → · more Wisconsin lake trips
Current Conditions
USGS snapshot Jul 6, 2026, 5:00 AM from gauge 05428000 (Lake Mendota at Madison, WI). Station page ↗ — a live reading replaces this snapshot when the gauge responds. Missing live data is not an all-clear.
Wisconsin DNR rates Panfish as abundant on Lake Mendota.
A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Lake Mendota D from EPA Water Quality Portal chemistry, and the water-quality trend over 7 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
WI DNR Lake Profile
Authoritative data from the Wisconsin DNR LakePages. 12 stations on file (most recent sample 2026).
Fish Species (DNR-rated)
DNR Reports & Resources
Wisconsin DNR Fisheries scientists publish multi-year survey reports for Lake Mendota covering fish populations, stocking, water quality, and management. 1 report on file.
These links open on the official state DNR websites (Wisconsin DNR survey PDFs · Minnesota DNR LakeFinder).
- —Lake Mendota gill netting survey, 2020-2024Netting Survey · WI DNR (PDF)
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | 83 ft |
| Surface Area | 9,781 acres |
| Public Access | Yes |
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS).
Recreation & Access
- Governor Nelson State ParkPublic
- Tenney ParkPublic
- Willow DrivePublic
- North Lake StreetPublic
- Warner ParkPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fish Species
Click a species to see every graded lake where it is documented.
Fishing Lake Mendota
Invasive & Introduced Species
Red chips are ecologically harmful invasive species. Gray chips are stocked or introduced fish that aren't a current ecological concern.
Water Quality Trend: ↓ Declining
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -7.88 m/yr | 2 |
| Phosphorus | → Stable | +0.68 µg/L/yr | 7 |
EPA Impairment Status
Lake Mendota is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit WI6876129 · Official waterbody report
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Lake Mendota under Clean Water Act (NPDES) discharge permits. 2 facilities have a reported Clean Water Act violation in the past three years.
- Wi Dnr Nevin Fish HatcheryFitchburg · 2 mi away · NPDES WI0002585Recent violation
- Uw Madison Charter Street Heating PlantMadison · 2 mi away · NPDES WI0038296Recent violation
- Dane County Regional AirportMadison · 4.3 mi away · NPDES WI0048747
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
County Ranking
Ranked #9 of 15 lakes in Dane County
Nearby Lakes With Higher Grades
Lake Mendota holds Grade D. 2 nearby lakes hold higher nutrient-and-algae grades — useful for a swim day, not a reason to skip lodging here.
See full comparison →Nearby Lakes in Dane County
Frequently asked questions about Lake Mendota
Where is Lake Mendota?
- Lake Mendota is a lake in Dane County, Wisconsin. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Lake Mendota?
- Lake Mendota in Dane County, Wisconsin has a water quality grade of D (Nutrient-rich). Water clarity: 5 ft visibility. Phosphorus: 65.4 µg/L. Maximum depth: 83 ft. Surface area: 9781 acres.
Is Lake Mendota safe to swim in?
- Nutrients and algae run higher than average — check local advisories before swimming, and skip the water if you see scum. Lake Mendota has a water quality grade of D (Nutrient-rich). Always check local health department advisories before swimming.
How deep is Lake Mendota?
- Lake Mendota has a maximum depth of 83 feet. The lake covers 9781 acres.
What fish are in Lake Mendota?
- Fish species found in Lake Mendota include Musky, Panfish, Largemouth Bass, Smallmouth Bass, Northern Pike, Walleye, Sturgeon, Catfish. Lake Mendota is located in Dane County, Wisconsin.
What did the DNR fisheries survey find at Lake Mendota?
- Wisconsin DNR rates Panfish as abundant on Lake Mendota. A DNR fisheries survey reports fish abundance and catch rates, not a water-quality grade. LakeQuality grades Lake Mendota D from EPA Water Quality Portal chemistry, and the water-quality trend over 7 years of monitoring is declining. Catch rate is not a swim clearance and is not a weekly bite report.
What is the water level at Lake Mendota?
- The USGS snapshot on this page for Lake Mendota is 850.06 ft of water-surface elevation, recorded Jul 6, 2026, 5:00 AM at gauge 05428000. Current Conditions hydrates a live NWIS reading from that same station when the gauge responds. A missed live fetch is not an all-clear.
Are there boat ramps on Lake Mendota?
- Lake Mendota has 5 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Governor Nelson State Park, Tenney Park, Willow Drive, North Lake Street, among others. Public access is listed as yes.
Explore Lake Mendota across LakeQuality
Depth, room, public access, and the state wake-sport rules
Fish species and top-graded lakes across Wisconsin
Fish species and best lakes in Dane County
Species activity outlook by water temperature and season
Top lakes and where to stay in the Madison Area Lakes area
Where to stay at Wisconsin's top lakes, each with its grade
Lakes in the Wisconsin River Watershed, ranked by water quality
High nutrients, frequent algae, reduced clarity
Wisconsin's cleanest and most-polluted lakes, ranked
More Wisconsin Lake Rankings
State Parks Near Lake Mendota
Other Grade D Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
Compare Lake Mendota With Nearby Lakes
Where this data comes from
377 measurements from 1 monitoring station, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX377 samples · 2020–2026
Analytical methods
- Phosphorus by Colorimetry
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Fish and recreation data from Wisconsin DNR Lakes
Named boat-access points from the USGS National Boat Ramps inventory