Grass Lake
Lake County, IllinoisView mapDirections
Nutrients and algae run well above the regional average.
↓ down from D at the last regrade
- Hypereutrophic
- Impaired · Mercury
- #13 of 19 in the county
- Public access
- Limited data
Grass Lake in Lake County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 1.4 ft visibility. Phosphorus: 103.5 µg/L. Chlorophyll-a (algae): 37.1 µg/L.
- Clarity
- 1.4 ft
- Type
- Hypereutrophic
- Public access
- Yes
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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 grade measures nutrients and algae, not lodging — cabins and rentals around Grass Lake are listed below.
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Grass Lake is a highly nutrient-loaded hypereutrophic lake in Lake County, Illinois. Water quality is graded F based on 1 sampling years through 2022. 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. Grade methodology: LakeQuality methodology.
What Grass Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch6 documented ramps
- Camping2 public campgrounds nearby
Swimming Safety
Grade onlyLimited data
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.
The F is nutrients and algae, 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.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.4 ft of visibility. Phosphorus 103.5 µg/L. Chlorophyll-a 37.1 µg/L. TSI 70. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.4 ft | Not graded |
| Phosphorus | 103.5 µg/L | Not graded |
| Chlorophyll-a (Algae) | 37.1 µg/L | Poor |
| Trophic State Index (TSI) | 70 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
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
Public campgrounds near Grass Lake
- Chain O' Lakes State Park Campground2.3 km
- Chain O' Lakes State Park Campground2.6 km
Nearest public campgrounds in the USGS National Map inventory, within about 3 miles. An empty list means USGS records no campground that close, which is not the same as camping being unavailable. Where the source gives an official reservation link, it is used; the cabin and hotel search does not cover campsites. More camping lakes
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
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.
County Ranking
Ranked #13 of 19 lakes in Lake County
Nearby Lakes in Lake County
Frequently asked questions about Grass Lake
Where is Grass Lake?
- Grass Lake is a lake in Lake County, Illinois. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Grass Lake?
- Grass Lake in Lake County, Illinois has a water quality grade of F (Algae-prone). 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?
- The F is nutrients and algae, 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.
Are there campgrounds on Grass Lake?
- Grass Lake has 2 public campgrounds from USGS The National Map within 5 km, including Chain O' Lakes State Park Campground, Chain O' Lakes State Park Campground. This is a location join, not a booking. Cabins and hotels are listed separately; campsite reservations use the official link when the source provides one.
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 grade
Very high nutrients, dense algae, poor clarity
Illinois's cleanest and most-polluted lakes, ranked
More Illinois Lake Rankings
Other Grade F 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)
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)
Named boat-access points from the USGS National Boat Ramps inventory
Public campgrounds from USGS The National Map Structures, within about 3 miles