Midlothian Lake
Cook County, Illinois30 acresView mapDirections
Nutrients and algae run well above the regional average.
↓ down from D at the last regrade
- Hypereutrophic
- Impaired · Mercury
- #16 of 16 in the county
- 49 ft max depth
- Limited data
Midlothian Lake in Cook County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 1.2 ft visibility. Phosphorus: 121 µg/L. Chlorophyll-a (algae): 61.5 µg/L. Surface area: 30 acres.
- Clarity
- 1.2 ft
- Typical in September
- 75°F
- Max depth
- ~49 ft est.
- Area
- 30 acres
- Type
- Hypereutrophic
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Stays near Midlothian Lake
Compare lakeside cabins, hotels, and vacation rentals near Midlothian 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 Midlothian Lake are listed below.
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Watch Midlothian Lake’s letter
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Midlothian Lake is a 30-acre highly nutrient-loaded hypereutrophic lake in Cook County, Illinois with an estimated average depth of about 49 feet. Water quality is graded F based on 2 sampling years through 2021. Compared to the 15 other monitored lakes in Cook County, Midlothian Lake ranks #16 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2021-09-21. 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. Midlothian Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), pesticides, pCBs. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1.2 ft of visibility. Phosphorus 121 µg/L. Chlorophyll-a 61.5 µg/L. TSI 73. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1.2 ft | Not graded |
| Phosphorus | 121 µg/L | Poor |
| Chlorophyll-a (Algae) | 61.5 µg/L | Poor |
| Trophic State Index (TSI) | 73 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Midlothian Lake typically sits around 75°F at the surface in September. Summer average is about 79°F. Usually warmest in Jul (about 81°F) and coldest in May (about 59°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 35 field readings (2016–2022) via the EPA Water Quality Portal. See the full Midlothian Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~49 ft est. |
| Average Depth | ~9 ft est. |
| Surface Area | 30 acres |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Illinois has not published bathymetry for Midlothian Lake.
Lake Size & Watershed
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.
Fishing Midlothian Lake
Reservoir Info (USACE NID)
Midlothian Lake is a man-made reservoir impounded by the Midlothian Creek Dam (completed 1975), built primarily for flood risk reduction on the MIDLOTHIAN CREEK; earth-type dam, 22 ft tall and 1,515 ft long.
- Surface area
- 30 ac
- Normal storage
- 148 ac-ft
- Max storage
- 1,279 ac-ft
- Drainage area
- 10.7 sq mi
- Hazard class
- High
- Owner
- ILLINOIS DEPARTMENT OF NATURAL RESOURCES
All listed purposes: Flood Risk Reduction;Recreation.
Source: USACE National Inventory of Dams, NID ID IL01002 · Operator website · Matched by proximity (0.3 km)
EPA Impairment Status
Midlothian 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_RHZI · Official waterbody report
County Ranking
Ranked #16 of 16 lakes in Cook County
Nearby Lakes in Cook County
Frequently asked questions about Midlothian Lake
Where is Midlothian Lake?
- Midlothian 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 Midlothian Lake?
- Midlothian Lake in Cook County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 1.2 ft visibility. Phosphorus: 121 µg/L. Chlorophyll-a (algae): 61.5 µg/L. Surface area: 30 acres.
Is Midlothian Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Midlothian Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), pesticides, pCBs. Check local advisories before you swim.
What is the water temperature of Midlothian Lake?
- Midlothian Lake typically sits around 75°F at the surface in September, from 35 EPA Water Quality Portal field readings (2016–2022). That is a typical value for the month, not a live reading.
How deep is Midlothian Lake?
- No published bathymetric survey covers Midlothian Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 49 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate. The lake covers 30 acres.
Explore Midlothian 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
Illinois's cleanest and most-polluted lakes, ranked
Planning a trip around Indiana Dunes?
Midlothian Lake is about 33 miles from Indiana Dunes National Park. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Indiana Dunes →More Illinois Lake Rankings
Other Grade F Lakes in Illinois
Hypereutrophic Lakes in Illinois
Where this data comes from
16 measurements from 1 monitoring station, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX16 samples · 2021
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (1)
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
Lake size & watershed from HydroLAKES (HydroSHEDS)