Bullfrog Lake
Cook County, IllinoisView mapDirections
Nutrients and algae run well above the regional average.
↓ down from D at the last regrade
- Hypereutrophic
- Impaired · Algal growth
- #13 of 16 in the county
- Limited data
Bullfrog Lake in Cook County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 1.4 ft visibility. Phosphorus: 73 µg/L. Chlorophyll-a (algae): 124.5 µg/L.
- Clarity
- 1.4 ft
- Typical in September
- 66°F
- Type
- Hypereutrophic
- Phosphorus
- 73 µg/L
- Chlorophyll-a
- 124.5 µg/L
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Stays near Bullfrog Lake
Compare lakeside cabins, hotels, and vacation rentals near Bullfrog 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Bullfrog Lake are listed below.
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Bullfrog Lake is a highly nutrient-loaded hypereutrophic lake in Cook County, Illinois. Water quality is graded F based on 2 sampling years through 2020. Compared to the 15 other monitored lakes in Cook County, Bullfrog Lake ranks #13 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2020-10-13. Grade methodology: LakeQuality methodology.
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. Bullfrog Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, noxious aquatic plants, nutrients (phosphorus, nitrogen), turbidity. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.4 ft of visibility. Phosphorus 73 µg/L. Chlorophyll-a 124.5 µg/L. TSI 72. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.4 ft | Not graded |
| Phosphorus | 73 µg/L | Poor |
| Chlorophyll-a (Algae) | 124.5 µg/L | Poor |
| Trophic State Index (TSI) | 72 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Bullfrog Lake typically sits around 66°F at the surface in September. Summer average is about 78°F. 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 →
Fishing Bullfrog Lake
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
County Ranking
Ranked #13 of 16 lakes in Cook County
Nearby Lakes in Cook County
Frequently asked questions about Bullfrog Lake
Where is Bullfrog Lake?
- Bullfrog Lake is a lake in Cook County, Illinois. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Bullfrog Lake?
- Bullfrog Lake in Cook County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 1.4 ft visibility. Phosphorus: 73 µg/L. Chlorophyll-a (algae): 124.5 µg/L.
Is Bullfrog Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Bullfrog Lake is listed impaired under Clean Water Act §303(d) (IR 5) for algal growth, noxious aquatic plants, nutrients (phosphorus, nitrogen), turbidity. Check local advisories before you swim.
What is the water temperature of Bullfrog Lake?
- Bullfrog Lake typically sits around 66°F at the surface in September, from 29 EPA Water Quality Portal field readings (2010–2023). That is a typical value for the month, not a live reading.
Explore Bullfrog Lake across LakeQuality
Species activity outlook by water temperature and season
Where to stay at Illinois's top lakes, each with its grade
Very high nutrients, dense algae, poor clarity
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Where this data comes from
32 measurements from 2 monitoring stations, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX32 samples · 2020
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