Otter Lake
Macoupin County, Illinois760 acresView mapDirections
Illinois EPA publishes the water-quality measurements for Otter Lake. Here is what has been measured.
- Hypereutrophic
- 48 ft max depth
- Public access
- Limited data
Otter Lake in Macoupin County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 1.8 ft visibility. Phosphorus: 81 µg/L. Chlorophyll-a (algae): 33.1 µg/L. Surface area: 760 acres.
Otter Lake is a 760-acre highly nutrient-loaded hypereutrophic lake in Macoupin County, Illinois with an estimated average depth of about 48 feet. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 2 other monitored lakes in Macoupin County, Otter Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2022-11-02. Methodology: how these readings are compared.
Otter Lake covers about 760 acres in Macoupin County. It has one public boat landing. For a place on the water, look through cabin and lake-house rentals near Otter Lake on Vrbo. For a hotel or motel room, Booking.com and Expedia both search around the lake.
What Otter Lake is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Otter Lake is safe to swim in today is a call for the Illinois Environmental Protection Agency and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Otter Lake
These are the measurements Illinois EPA publishes for Otter Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 1.8 ft of visibility. Phosphorus 81 µg/L. Chlorophyll-a 33.1 µg/L. TSI 67.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 1.8ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 81µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 33.1µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 67 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Otter Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Otter Lake typically sits around 64°F at the surface in October. Summer average is about 75°F. Usually warmest in Jul (about 76°F) and coldest in Nov (about 57°F). These are typical values by month — not a live reading.
Column height runs from this lake’s coldest month (57°F) to its warmest (76°F).
Typical surface water temperature by month, from 235 field readings (2011–2022) via the EPA Water Quality Portal. See the full Otter Lake water temperature breakdown →
Lake Details
Max depth
~48 ft est.
Surface area
760 acres
Public access
Yes
Listed by Illinois EPA
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Illinois has not published bathymetry for Otter Lake.
Lake Size & Watershed
Watershed (drainage) area
21 sq mi
HydroLAKES / HydroSHEDS
Shoreline
15 mi
HydroLAKES / HydroSHEDS
Elevation
633 ft
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
- Otter Lake ParkPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Otter Lake
Compare lakeside cabins, hotels, and vacation rentals near Otter Lake in Macoupin 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 readings cover nutrients and algae, not lodging. Cabins and rentals around Otter Lake are listed below.
Top-rated places to stay near Otter Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
Availability and prices from Stay22 partners (Booking.com, Vrbo, Expedia). We may earn a commission from bookings, at no extra cost to you.
Planning a trip? Cabins and lodging at Otter Lake → · more Illinois lake trips
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Fishing Otter Lake
Reservoir Info (USACE NID)
Otter Lake is a man-made reservoir impounded by the Otter Lake Dam (completed 1969), built primarily for recreation on the WEST FORK OTTER CREEK; earth-type dam, 71 ft tall and 1,010 ft long.
- Surface area
- 760 ac
- Normal storage
- 15,563 ac-ft
- Max storage
- 24,708 ac-ft
- Drainage area
- 20.2 sq mi
- Hazard class
- Significant
- Owner
- OTTER LAKE WATER COMMISSION
All listed purposes: Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID IL00133 · Operator website
Regulated Pollution Sources Nearby
2 EPA-permitted facilities operate within about 5 miles of Otter Lake under Clean Water Act (NPDES) discharge permits.
- Otter Lake Wtr Commission WtpGirard · 0.4 mi away · NPDES IL0042552
- Christopher Bruley Private Sewage Disposal SystemGirard · 2.7 mi away · NPDES IL0080167
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.
Nearby Lakes in Macoupin County
Frequently asked questions about Otter Lake
Where is Otter Lake?
- Otter Lake is a lake in Macoupin County, Illinois. Its water-quality measurements are published by Illinois EPA and shown on this page as reported.
What is the water quality of Otter Lake?
- Otter Lake in Macoupin County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Water clarity: 1.8 ft visibility. Phosphorus: 81 µg/L. Chlorophyll-a (algae): 33.1 µg/L. Surface area: 760 acres.
Is Otter Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
What is the water temperature of Otter Lake?
- Otter Lake typically sits around 64°F at the surface in October, from 235 EPA Water Quality Portal field readings (2011–2022). That is a typical value for the month, not a live reading.
How deep is Otter Lake?
- No published bathymetric survey covers Otter Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 48 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 760 acres.
Are there boat ramps on Otter Lake?
- Otter Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Otter Lake Park. Public access is listed as yes.
Can I fish at Otter Lake?
- Otter Lake has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Illinois's fish and wildlife agency, so check its current regulations before you go.
Explore Otter Lake across LakeQuality
Depth, room, public access, and the state wake-sport rules
Species activity outlook by water temperature and season
Where to stay at Illinois's top lakes, each with its readings
Illinois's cleanest lakes, ranked on agency measurements
More lakes in Illinois
Other Lakes in Illinois
Hypereutrophic Lakes in Illinois
Compare Otter Lake With Nearby Lakes
Where this data comes from
60 measurements from 4 monitoring stations, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- illinois epa
IL_EPA_WQX60 samples · 2022
Analytical methods
- MEASURED IN FIELD
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (4)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
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