Salem Lake
Marion County, Illinois78 acresView mapDirections
Nutrients and algae run well above the regional average.
- Hypereutrophic
- Impaired · Mercury
- #1 of 6 in the county
- 46 ft max depth
- Public access
Salem Lake in Marion County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 1 ft visibility. Phosphorus: 234 µg/L. Chlorophyll-a (algae): 77.5 µg/L. Surface area: 78 acres.
- Clarity
- 1 ft
- Typical in August
- 81°F
- Max depth
- ~46 ft est.
- Area
- 78 acres
- Type
- Hypereutrophic
- Phosphorus
- 234 µg/L
- Chlorophyll-a
- 77.5 µg/L
- Trend
- ↑ Improving
- Public access
- Yes
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Stays near Salem Lake
Compare lakeside cabins, hotels, and vacation rentals near Salem Lake in Marion 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 Salem Lake are listed below.
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Watch Salem Lake’s letter
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Salem Lake is a 78-acre highly nutrient-loaded hypereutrophic lake in Marion County, Illinois with an estimated average depth of about 46 feet. Water quality is graded F 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 5 other monitored lakes in Marion County, Salem Lake ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2022-10-19. Grade methodology: LakeQuality methodology.
What Salem Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
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. Salem Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity, turbidity. Check local advisories before you swim.
Water Quality Grade: F (Algae-prone)
Very murky, less than 1 ft of visibility. Phosphorus 234 µg/L. Chlorophyll-a 77.5 µg/L. TSI 78. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 1 ft | Not graded |
| Phosphorus | 234 µg/L | Poor |
| Chlorophyll-a (Algae) | 77.5 µg/L | Poor |
| Trophic State Index (TSI) | 78 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Water Temperature
Salem Lake typically sits around 81°F at the surface in August. Summer average is about 81°F. Usually warmest in Jul (about 82°F) and coldest in Oct (about 58°F). These are typical values by month — not a live reading.
Typical surface water temperature by month, from 234 field readings (2010–2022) via the EPA Water Quality Portal. See the full Salem Lake water temperature breakdown →
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~46 ft est. |
| Average Depth | ~7 ft est. |
| Surface Area | 78 acres |
| 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 Salem 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
- Salem ReservoirPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Fishing Salem Lake
Water Quality Trend: ↑ Improving
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +1 m/yr | 2 |
| Phosphorus | ↑ Improving | -14 µg/L/yr | 2 |
| Chlorophyll-a | → Stable | +1.05 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Salem Lake is a man-made reservoir impounded by the Salem Reservoir Dam (completed 1912), built primarily for recreation on the TOWN CREEK; earth-type dam, 21 ft tall and 775 ft long.
- Surface area
- 78 ac
- Normal storage
- 388 ac-ft
- Max storage
- 900 ac-ft
- Drainage area
- 3.9 sq mi
- Hazard class
- High
- Owner
- CITY OF SALEM
All listed purposes: Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID IL00245 · Operator website
EPA Impairment Status
Salem Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IL_ROR · Official waterbody report
Regulated Pollution Sources Nearby
3 EPA-permitted facilities operate within about 5 miles of Salem 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.
- Salem Stp, City OfSalem · 2.1 mi away · NPDES IL0023264MajorRecent violation
- Union Pacific Railroad-SalemSalem · 1.7 mi away · NPDES IL0000361
- Salem Municipal Landfill #2Salem · 2 mi away · NPDES IL0075621
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 #1 of 6 lakes in Marion County
Nearby Lakes in Marion County
Frequently asked questions about Salem Lake
Where is Salem Lake?
- Salem Lake is a lake in Marion County, Illinois. LakeQuality grades it F for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Salem Lake?
- Salem Lake in Marion County, Illinois has a water quality grade of F (Algae-prone). Water clarity: 1 ft visibility. Phosphorus: 234 µg/L. Chlorophyll-a (algae): 77.5 µg/L. Surface area: 78 acres.
Is Salem Lake safe to swim in?
- The F is nutrients and algae, not a swimming clearance. Salem Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity, turbidity. Check local advisories before you swim.
What is the water temperature of Salem Lake?
- Salem Lake typically sits around 81°F at the surface in August, from 234 EPA Water Quality Portal field readings (2010–2022). That is a typical value for the month, not a live reading.
How deep is Salem Lake?
- No published bathymetric survey covers Salem Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 46 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 78 acres.
Are there boat ramps on Salem Lake?
- Salem Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Salem Reservoir. Public access is listed as yes.
Explore Salem 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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Other Grade F Lakes in Illinois
Hypereutrophic Lakes in Illinois
Where this data comes from
102 measurements from 3 monitoring stations, 2020–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX102 samples · 2020–2022
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (3)
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