Grass Lake
Lake County, IllinoisView mapDirections
Illinois EPA publishes the water-quality measurements for Grass Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Mercury
- Public access
- Limited data
Grass Lake in Lake County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 1.4 ft visibility. Phosphorus: 103.5 µg/L. Chlorophyll-a (algae): 37.1 µg/L.
Grass Lake is a highly nutrient-loaded hypereutrophic lake in Lake County, Illinois. Limited fish-species data available. Public access is available with 6 public boat landings. Compared to the 18 other monitored lakes in Lake County, Grass Lake ranks #13 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2022-10-26. Methodology: how these readings are compared.
Grass Lake has 6 public boat landings, so a lakefront rental is not the only way to get a boat on the water. Vrbo is where to look for cabins and lake homes around Grass Lake, and Booking.com and Expedia search hotels near the lake for your dates.
What Grass Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch6 documented ramps
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Grass Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), pesticides, pCBs, turbidity. Check local advisories before you swim.
Whether Grass Lake is safe to swim in today is a call for the Illinois Environmental Protection Agency and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Grass Lake
These are the measurements Illinois EPA publishes for Grass Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1.4 ft of visibility. Phosphorus 103.5 µg/L. Chlorophyll-a 37.1 µg/L. TSI 70.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.4ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 104µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 37.1µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 70 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Grass Lake
Answers come straight from the public measurements and survey records on this page.
Recreation & Access
- Dolphin HarborPublic
- Grass Lake Marina and RV parkPublic
- Maple GrovePublic
- a marinaSemi-private
- a marinaSemi-private
- North Jackson DriveSemi-private
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Grass Lake
Compare lakeside cabins, hotels, and vacation rentals near Grass Lake in Lake County, Illinois — 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 readings cover nutrients and algae, not lodging. Cabins and rentals around Grass Lake are listed below.
Top-rated places to stay near Grass Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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 Grass Lake → · more Illinois lake trips
Follow Grass Lake’s readings
Email me when new measurements post for this lake. Updates stay free.
Or email
Fishing Grass Lake
EPA Impairment Status
Grass Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Fish consumption, Other.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IL_RTQ · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Grass Lake under Clean Water Act (NPDES) discharge permits.
- Fox Lake Grade School Dist 114Spring Grove · 1.3 mi away · NPDES IL0076597
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.
Nearby Lakes in Lake County
Frequently asked questions about Grass Lake
Where is Grass Lake?
- Grass Lake is a lake in Lake County, Illinois. Its water-quality measurements are published by Illinois EPA and shown on this page as reported.
What is the water quality of Grass Lake?
- Grass Lake in Lake County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 1.4 ft visibility. Phosphorus: 103.5 µg/L. Chlorophyll-a (algae): 37.1 µg/L.
Is Grass Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Grass Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), pesticides, pCBs, turbidity. Check local advisories before you swim.
Are there boat ramps on Grass Lake?
- Grass Lake has 6 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Dolphin Harbor, Grass Lake Marina and RV park, Maple Grove, a marina, among others. Public access is listed as yes.
Can I fish at Grass Lake?
- Grass Lake has 6 documented boat landings in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Illinois's fish and wildlife agency, so check its current regulations before you go.
Explore Grass Lake across LakeQuality
Species activity outlook by water temperature and season
Top lakes and where to stay in the Chain O'Lakes area
Where to stay at Illinois's top lakes, each with its readings
Illinois's cleanest lakes, ranked on agency measurements
More lakes in Illinois
Other Lakes in Illinois
Hypereutrophic Lakes in Illinois
Where this data comes from
20 measurements from 2 monitoring stations, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX20 samples · 2022
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (2)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Named boat-access points from the USGS National Boat Ramps inventory