Mauvaise Terre Lake
Morgan County, Illinois262 acresView mapDirections
Illinois EPA publishes the water-quality measurements for Mauvaise Terre Lake. Here is what has been measured.
- Hypereutrophic
- Impaired · Mercury
- 29 ft max depth
- Limited data
Mauvaise Terre Lake in Morgan County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Phosphorus: 163.5 µg/L. Chlorophyll-a (algae): 62 µg/L. Surface area: 262 acres.
Mauvaise Terre Lake is a 262-acre highly nutrient-loaded hypereutrophic lake in Morgan County, Illinois with an estimated average depth of about 29 feet. Compared to the 1 other monitored lakes in Morgan County, Mauvaise Terre Lake ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Illinois EPA, last sampled 2021-10-04. Methodology: how these readings are compared.
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. Mauvaise Terre Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, metals (other than mercury), nutrients (phosphorus, nitrogen), turbidity. Check local advisories before you swim.
Whether Mauvaise Terre 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 Mauvaise Terre Lake
These are the measurements Illinois EPA publishes for Mauvaise Terre Lake, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 163.5 µg/L. Chlorophyll-a 62 µg/L. TSI 74.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 164µg/L | Poor GoodFairPoor |
| Chlorophyll-a (algae) | 62µg/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. | 74 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Mauvaise Terre Lake
Answers come straight from the public measurements and survey records on this page.
Water Temperature
Mauvaise Terre Lake typically sits around 68°F at the surface in October. Summer average is about 79°F. Usually warmest in Jul (about 84°F) and coldest in Apr (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 (84°F).
Typical surface water temperature by month, from 38 field readings (2011–2021) via the EPA Water Quality Portal. See the full Mauvaise Terre Lake water temperature breakdown →
Lake Details
Max depth
~29 ft est.
Surface area
262 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 Mauvaise Terre Lake.
Lake Size & Watershed
Watershed (drainage) area
33 sq mi
HydroLAKES / HydroSHEDS
Shoreline
3.8 mi
HydroLAKES / HydroSHEDS
Elevation
597 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.
Stays via Stay22
Stays near Mauvaise Terre Lake
Compare lakeside cabins, hotels, and vacation rentals near Mauvaise Terre Lake in Morgan 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 Mauvaise Terre Lake are listed below.
Top-rated places to stay near Mauvaise Terre Lake
Prices for Oct 23–25, 4 adults. Change dates on the map below.
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Fishing Mauvaise Terre Lake
Reservoir Info (USACE NID)
Mauvaise Terre Lake is a man-made reservoir impounded by the Mauvaise Terre Lake Dam (completed 1923), built primarily for recreation on the MAUVAISE TERRE CREEK; earth-type dam, 30 ft tall and 850 ft long.
- Surface area
- 262 ac
- Normal storage
- 628 ac-ft
- Max storage
- 5,624 ac-ft
- Drainage area
- 34.3 sq mi
- Hazard class
- High
- Owner
- CITY OF JACKSONVILLE
All listed purposes: Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID IL00709 · Operator website
EPA Impairment Status
Mauvaise Terre Lake is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Drinking water, Fish consumption, Other.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit IL_SDL · Official waterbody report
Regulated Pollution Sources Nearby
1 EPA-permitted facility operate within about 5 miles of Mauvaise Terre 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.
- Jacksonville Stp, City OfJacksonville · 2.4 mi away · NPDES IL0021661MajorRecent 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.
Nearby Lakes in Morgan County
Frequently asked questions about Mauvaise Terre Lake
Where is Mauvaise Terre Lake?
- Mauvaise Terre Lake is a lake in Morgan County, Illinois. Its water-quality measurements are published by Illinois EPA and shown on this page as reported.
What is the water quality of Mauvaise Terre Lake?
- Mauvaise Terre Lake in Morgan County, Illinois has water-quality measurements published by Illinois EPA, shown here as reported. Phosphorus: 163.5 µg/L. Chlorophyll-a (algae): 62 µg/L. Surface area: 262 acres.
Is Mauvaise Terre Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Mauvaise Terre Lake is listed impaired under Clean Water Act §303(d) (IR 5) for mercury, metals (other than mercury), nutrients (phosphorus, nitrogen), turbidity. Check local advisories before you swim.
What is the water temperature of Mauvaise Terre Lake?
- Mauvaise Terre Lake typically sits around 68°F at the surface in October, from 38 EPA Water Quality Portal field readings (2011–2021). That is a typical value for the month, not a live reading.
How deep is Mauvaise Terre Lake?
- No published bathymetric survey covers Mauvaise Terre Lake, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 29 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 262 acres.
Explore Mauvaise Terre Lake across LakeQuality
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Where this data comes from
20 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_WQX20 samples · 2021
Analytical methods
- Phosphorus by Colorimetry
- 10200 H 2 ~ Chlorophyll a-b-c Determination by spectrophotometer
Monitoring station identifiers (1)
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
Impairment status from EPA ATTAINS 303(d) database
Regulated discharger data from EPA ECHO (ICIS-NPDES)
Lake size & watershed from HydroLAKES (HydroSHEDS)