Diversey Harbor Lake is a cold, clear oligotrophic lake in Cook County, Illinois. Water quality is graded A based on 1 sampling years through 2023. Compared to the 67 other monitored lakes in Cook County, Diversey Harbor Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2023-05-23. Grade methodology: LakeGrade methodology.
Watch Diversey Harbor Lake water quality
Subscribe for LakeQuality updates by email. No spam, unsubscribe anytime.
Swimming Safety
Excellent for swimming, crystal clear water with minimal algae
Water Quality Grade: A, Excellent
Crystal clear, you can see 25.6 ft down. Trophic State Index: 30.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 25.6 ft | A |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 30 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Diversey Harbor Lake
Compare lakeside cabins, hotels, and vacation rentals near Diversey Harbor Lake in Cook 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.
Top-rated places to stay near Diversey Harbor Lake
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 to Diversey Harbor Lake?
Get lake water-quality report cards plus the best cabin & lodging deals near Diversey Harbor Lake — straight to your inbox. No spam, unsubscribe anytime.
Planning a whole trip? See where to stay at Illinois’s top lakes →
Fishing Diversey Harbor Lake
Water Temperature
Diversey Harbor Lake averages about 67°F at the surface in summer, usually warmest in Sep (about 73°F) and coldest in Nov (about 56°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 13 field readings (2013–2023) via the EPA Water Quality Portal. See the full Diversey Harbor Lake water temperature breakdown →
Location
County Ranking
Ranked #1 of 68 lakes in Cook County
Nearby Lakes in Cook County
Explore Diversey Harbor Lake across LakeGrade
Species activity outlook by water temperature and season
Where to stay at Illinois's top lakes, each with its grade
Low nutrients, clear water, excellent for swimming
Illinois's cleanest and most-polluted lakes, ranked
More Illinois Lake Rankings
Other Grade A Lakes in Illinois
Oligotrophic Lakes in Illinois
More records, surveys & data sources
EPA Impairment Status
Diversey Harbor Lake 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 IL_QZI · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Most recent sample: 2023-05-23
Monitoring stations: 1