Long Lake is a productive, nutrient-rich eutrophic lake in Lake County, Illinois. Water quality is graded D based on 2 sampling years through 2022. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 15 other monitored lakes in Lake County, Long Lake ranks #11 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois DNR, last sampled 2022-10-12. Grade methodology: LakeGrade methodology.
Watch Long Lake water quality
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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 2.9 ft of visibility. Phosphorus level: 41.5 µg/L. Trophic State Index: 60.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.9 ft | F |
| Phosphorus | 41.5 µg/L | C |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 60 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Long Lake
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Fishing Long Lake
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -31.1 m/yr | 2 |
| Phosphorus | ↑ Improving | -6.5 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -18.1 µg/L/yr | 2 |
Recreation & Access
Water Temperature
Long Lake averages about 76°F at the surface in summer, usually warmest in Jul (about 79°F) and coldest in May (about 60°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 237 field readings (2012–2022) via the EPA Water Quality Portal. See the full Long Lake water temperature breakdown →
Location
County Ranking
Ranked #11 of 16 lakes in Lake County
Cleaner Lakes Within 30 Miles
Long Lake holds Grade D. 2 nearby lakes hold higher grades.
- BRound LakeLake County · 2.6 mi · Two grade letters higher (D → B)
- BGrays LakeLake County · 4.6 mi · Two grade letters higher (D → B)
Nearby Lakes in Lake County
Explore Long Lake across LakeGrade
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 grade
High nutrients, frequent algae, reduced clarity
Illinois's cleanest and most-polluted lakes, ranked
More Illinois Lake Rankings
Other Grade D Lakes in Illinois
Eutrophic Lakes in Illinois
More records, surveys & data sources
EPA Impairment Status
Long 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_RTJ · Official waterbody report
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth is a modeled estimate.
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Long Lake under Clean Water Act (NPDES) discharge permits, including 1 classified by the EPA as major discharger. 1 facility has a reported Clean Water Act violation in the past three years.
- Baxter Healthcare CorporationRound Lake · 2.6 mi away · NPDES IL0024074Major
- Camp Hickory StpIngleside · 1.8 mi away · NPDES IL0046043Recent violation
Facilities permitted to discharge under the Clean Water Act within ~5 miles; proximity does not by itself mean a facility affects this lake. Source: EPA ECHO (ICIS-NPDES), as of 2026-07.
Data Sources
Water quality data from the EPA Water Quality Portal
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grading methodology based on Metropolitan Council standards
Public boat-access points from the USGS National Boat Ramps inventory
Most recent sample: 2022-10-12
Monitoring stations: 3