Long Lake
Lake County, IllinoisView mapDirections
Nutrients and algae run well above the regional average.
↓ down from D at the last regrade
- Hypereutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #12 of 19 in the county
- 53 ft max depth
- Public access
Long Lake in Lake County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 3.4 ft visibility. Phosphorus: 81 µg/L. Chlorophyll-a (algae): 57.1 µg/L.
- Clarity
- 3.4 ft
- Typical in September
- 74°F
- Max depth
- ~53 ft est.
- Type
- Hypereutrophic
- Trend
- ↑ Improving
- Public access
- Yes
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Stays near Long Lake
Compare lakeside cabins, hotels, and vacation rentals near Long Lake in Lake 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 Long Lake are listed below.
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Long Lake is a highly nutrient-loaded hypereutrophic lake in Lake County, Illinois with an estimated average depth of about 53 feet. Water quality is graded F based on 2 sampling years through 2024. Overall water quality is improving over recent sampling years. Limited fish-species data available. Public access is available with 2 public boat landings. Compared to the 18 other monitored lakes in Lake County, Long Lake ranks #12 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2024-02-21. Grade methodology: LakeQuality methodology.
What Long Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch2 documented ramps
Swimming Safety
Grade onlyAlgae risk
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. Long Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Murky, only visible to about 3.4 ft. Phosphorus 81 µg/L. Chlorophyll-a 57.1 µg/L. TSI 66. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 3.4 ft | Not graded |
| Phosphorus | 81 µg/L | Poor |
| Chlorophyll-a (Algae) | 57.1 µg/L | Poor |
| Trophic State Index (TSI) | 66 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Current Conditions
USGS snapshot Jul 1, 2026, 4:30 PM from gauge 423784088133401 (Long Lake at Ben Dock at Long Lake, IL). Station page ↗ — a live reading replaces this snapshot when the gauge responds. Missing live data is not an all-clear.
Water Temperature
Long Lake typically sits around 74°F at the surface in September. Summer average is about 76°F. Usually warmest in Jul (about 80°F) and coldest in Feb (about 38°F). These are typical values by month — see Current Conditions above for the latest gauge reading.
Typical surface water temperature by month, from 177 field readings (2012–2024) via the EPA Water Quality Portal. See the full Long Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~53 ft est. |
| Average Depth | ~14 ft est. |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Illinois has not published bathymetry for Long 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.
Recreation & Access
- Long Lake boat launchPublic
- Swanys On Long Lake MarinaPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
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 | -26.5 µg/L/yr | 2 |
| Chlorophyll-a | ↑ Improving | -18.8 µg/L/yr | 2 |
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
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Long Lake under Clean Water Act (NPDES) discharge permits. 1 facility has a reported Clean Water Act violation in the past three years.
- Camp Henry Horner StpIngleside · 2.1 mi away · NPDES IL0054615Recent 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.
County Ranking
Ranked #12 of 19 lakes in Lake County
Nearby Lakes in Lake County
Frequently asked questions about Long Lake
Where is Long Lake?
- Long Lake is a lake in Lake County, Illinois. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Long Lake?
- Long Lake in Lake County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 3.4 ft visibility. Phosphorus: 81 µg/L. Chlorophyll-a (algae): 57.1 µg/L.
Is Long Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Long Lake is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
What is the water temperature of Long Lake?
- Long Lake typically sits around 74°F at the surface in September, from 177 EPA Water Quality Portal field readings (2012–2024). That is a typical value for the month, not a live reading. A USGS gauge on this lake last read 83°F.
How deep is Long Lake?
- No published bathymetric survey covers Long Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 53 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Are there boat ramps on Long Lake?
- Long Lake has 2 documented boat landings in the USGS National Boat Ramps inventory. Named access points include Long Lake boat launch, Swanys On Long Lake Marina. Public access is listed as yes.
Explore Long Lake across LakeQuality
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
Very high nutrients, dense algae, poor clarity
Illinois's cleanest and most-polluted lakes, ranked
More Illinois Lake Rankings
Other Grade F Lakes in Illinois
Hypereutrophic Lakes in Illinois
Where this data comes from
76 measurements from 4 monitoring stations, 2022–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Illinois Water Science Center
USGS-IL40 samples · 2022–2024 - illinois epa
IL_EPA_WQX36 samples · 2022
Analytical methods
- Secchi disk method
- Nutrients, wu, WCA,persulfate,CF
- Plant pigments, sonication & 445
- YSI EXO turbidity sensor, FNU
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (4)
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
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory