Diamond Lake
Lake County, IllinoisView mapDirections
Illinois EPA publishes the water-quality measurements for Diamond Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Noxious aquatic plants
- 38 ft max depth
- Public access
- Limited data
Diamond Lake in Lake County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Chlorophyll-a (algae): 63.6 µg/L.
Diamond Lake is a highly nutrient-loaded hypereutrophic lake in Lake County, Illinois with an estimated average depth of about 38 feet. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 18 other monitored lakes in Lake County, Diamond Lake ranks #16 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2020-09-23. Methodology: how these readings are compared.
What Diamond Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
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. Diamond Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for noxious aquatic plants, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Diamond 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 Diamond Lake
These are the measurements Illinois EPA publishes for Diamond Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Chlorophyll-a 63.6 µg/L. TSI 71.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | 63.6µg/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. | 71 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Diamond Lake
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~38 ft est.
Public access
Yes
Listed by Illinois EPA
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Illinois has not published bathymetry for Diamond Lake.
Lake Size & Watershed
Watershed (drainage) area
0 sq mi
HydroLAKES / HydroSHEDS
Surface area
141 acres
HydroLAKES / HydroSHEDS
Shoreline
2 mi
HydroLAKES / HydroSHEDS
Elevation
745 ft
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
- Diamond LakePublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Diamond Lake
Compare lakeside cabins, hotels, and vacation rentals near Diamond 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 Diamond Lake are listed below.
Top-rated places to stay near Diamond Lake
Prices for Nov 6–8, 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 whole trip? See where to stay at Illinois’s top lakes →
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Fishing Diamond Lake
EPA Impairment Status
Diamond Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
Designated uses not supporting: Other.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IL_RGB · Official waterbody report
Nearby Lakes in Lake County
Frequently asked questions about Diamond Lake
Where is Diamond Lake?
- Diamond 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 Diamond Lake?
- Diamond Lake in Lake County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Chlorophyll-a (algae): 63.6 µg/L.
Is Diamond Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Diamond Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for noxious aquatic plants, nutrients (phosphorus, nitrogen). Check local advisories before you swim.
How deep is Diamond Lake?
- No published bathymetric survey covers Diamond Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 38 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Are there boat ramps on Diamond Lake?
- Diamond Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Diamond Lake. Public access is listed as yes.
Can I fish at Diamond Lake?
- Diamond Lake has 1 documented boat landing 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 Diamond 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
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Other Lakes in Illinois
Hypereutrophic Lakes in Illinois
Where this data comes from
10 measurements from 1 monitoring station, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX10 samples · 2020
Analytical methods
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (1)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory