Lake Monona
Lake Monona in Dane County, Wisconsin has a water quality grade of D (Nutrient-rich). Water clarity: 7 ft visibility. Phosphorus: 98.5 µg/L.
- Clarity
- 7 ft
- Typical in August
- 76°F
- Mean depth
- ~22 ft est.
- Type
- Eutrophic
- Trend
- → Stable
- 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 Monona →
Next lake in Dane County
Lake Monona is a productive, nutrient-rich eutrophic lake in Dane County, Wisconsin with an estimated average depth of about 22 feet. Water quality is graded D based on 1 sampling years through 2026. Water clarity is improving over recent sampling years. Limited fish-species data available. Public access is available with 7 public boat landings. Compared to the 14 other monitored lakes in Dane County, Lake Monona ranks #8 for water quality.
Source: EPA Water Quality Portal sampling records, Wisconsin DNR Surface Water, last sampled 2026-06-25. Grade methodology: LakeGrade methodology.
Watch Lake Monona water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Lake Monona Water Quality Report Card (2026)
A printable one-page report card for Lake Monona: 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)
Moderate clarity, visible to about 7 ft. Phosphorus level: 98.5 µg/L. Trophic State Index: 60.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 7 ft | Not graded |
| Phosphorus | 98.5 µg/L | Poor |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 60 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Lake Monona
Compare lakeside cabins, hotels, and vacation rentals near Lake Monona 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 Monona are listed below.
Top-rated places to stay near Lake Monona
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 whole trip? See where to stay at Wisconsin’s top lakes →
Current Conditions
USGS snapshot Jul 6, 2026, 5:00 AM from gauge 05429000 (Lake Monona at Madison, WI). Station page ↗ — a live reading replaces this snapshot when the gauge responds. Missing live data is not an all-clear.
Water Temperature
Lake Monona typically sits around 76°F at the surface in August. Summer average is about 77°F. Usually warmest in Jul (about 78°F) and coldest in Jun (about 76°F). These are typical values by month — see Current Conditions above for the latest gauge reading.
Typical surface water temperature by month, from 18 field readings (2024–2025) via the EPA Water Quality Portal. See the full Lake Monona water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~22 ft est. |
| Public Access | Yes |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Wisconsin has not published bathymetry for Lake Monona.
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Recreation & Access
- Law ParkPublic
- Olbrich ParkPublic
- Tonyawatha ParkPublic
- Olin-Turville ParkPublic
- Lottes ParkPublic
- Burr Jones ParkPublic
Showing 6 of 7 documented landings from the USGS National Boat Ramps inventory.
Fishing Lake Monona
Water Quality Trend: → Stable
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.679 m/yr | 6 |
| Phosphorus | ↓ Declining | +11.04 µg/L/yr | 7 |
EPA Impairment Status
Lake Monona is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit WI10001455 · Official waterbody report
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Lake Monona under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 2 facilities have a reported Clean Water Act violation in the past three years.
- Madison Metro Sew Dist WwtfMadison · 1.8 mi away · NPDES WI0024597MajorRecent violation
- Madison Gas & Electric Blount StationMadison · 0.9 mi away · NPDES WI0001961Recent violation
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 #8 of 15 lakes in Dane County
Nearby Lakes With Higher Grades
Lake Monona 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 Monona
What is the water quality grade for Lake Monona?
- Lake Monona in Dane County, Wisconsin has a water quality grade of D (Nutrient-rich). Water clarity: 7 ft visibility. Phosphorus: 98.5 µg/L.
Is Lake Monona 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 Monona has a water quality grade of D (Nutrient-rich). Always check local health department advisories before swimming.
What is the water temperature of Lake Monona?
- Lake Monona typically sits around 76°F at the surface in August, from 18 EPA Water Quality Portal field readings (2024–2025). That is a typical value for the month, not a live reading. A USGS gauge on this lake last read 78°F.
How deep is Lake Monona?
- No published bathymetric survey covers Lake Monona, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 22 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
What is the water level at Lake Monona?
- The USGS snapshot on this page for Lake Monona is 845.04 ft of water-surface elevation, recorded Jul 6, 2026, 5:00 AM at gauge 05429000. 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 Monona?
- Lake Monona has 7 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Law Park, Olbrich Park, Tonyawatha Park, Olin-Turville Park, among others. Public access is listed as yes.
Explore Lake Monona across LakeGrade
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 Monona
Other Grade D Lakes in Wisconsin
Eutrophic Lakes in Wisconsin
Where this data comes from
321 measurements from 2 monitoring stations, 2020–2026. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Wisconsin Department of Natural Resources
WIDNR_WQX321 samples · 2020–2026
Analytical methods
- Phosphorus by Colorimetry
Monitoring station identifiers (2)
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)
Named boat-access points from the USGS National Boat Ramps inventory