Bullfrog Lake is a productive, nutrient-rich eutrophic lake in Cook County, Illinois. Water quality is graded D based on 2 sampling years through 2020. Compared to the 67 other monitored lakes in Cook County, Bullfrog Lake ranks #39 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2020-10-13. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 1.4 ft of visibility. Phosphorus level: 40.5 µg/L. Trophic State Index: 65.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.4 ft | F |
| Phosphorus | 40.5 µg/L | C |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 65 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Bullfrog Lake
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Fishing Bullfrog Lake
Water Temperature
Bullfrog Lake averages about 78°F at the surface in summer, usually warmest in Aug (about 81°F) and coldest in Oct (about 60°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 29 field readings (2010–2023) via the EPA Water Quality Portal. See the full Bullfrog Lake water temperature breakdown →
Location
County Ranking
Ranked #39 of 68 lakes in Cook County
Cleaner Lakes Within 30 Miles
Bullfrog Lake holds Grade D. 2 nearby lakes hold higher grades.
- CSag Quarry East LakeCook County · 1.9 mi · Higher grade (D → C)
- CSag Quarry West LakeCook County · 2.1 mi · Higher grade (D → C)
Nearby Lakes in Cook County
Explore Bullfrog Lake across LakeGrade
More Illinois Lake Rankings
Other Grade D Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
Reservoir Info (USACE NID)
Bullfrog Lake is a man-made reservoir impounded by the Bullfrog Lake Dam (completed 1958), built primarily for recreation on the TRIB DES PLAINES RIVER; earth-type dam, 17 ft tall and 700 ft long.
- Normal storage
- 77 ac-ft
- Max storage
- 144 ac-ft
- Hazard class
- Significant
- Owner
- FOREST PRESERVE DISTRICT OF COOK COUNTY
Source: USACE National Inventory of Dams, NID ID IL00869 · Operator website
EPA Impairment Status
Bullfrog Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit IL_RHZF · Official waterbody report
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Grading methodology based on Metropolitan Council standards
Most recent sample: 2020-10-13
Monitoring stations: 2