Flat Lake
Marshall County, Indiana57 acresView mapDirections
IDEM publishes the water-quality measurements for Flat Lake. Here is what has been measured.
- Impaired · Nutrients (phosphorus, nitrogen)
- Limited data
Flat Lake in Marshall County, Indiana has water-quality measurements published by IDEM, shown here as reported. Phosphorus: 367.8 µg/L. Chlorophyll-a (algae): 40.7 µg/L. Surface area: 57 acres.
Flat Lake is a 57-acre lake in Marshall County, Indiana.
Source: EPA Water Quality Portal sampling records, IDEM, last sampled 2023-08-01. Methodology: how these readings are compared.
Swimming conditions
No readingRecreation use not supported
Nutrient and algae readings are not a swimming clearance. Flat Lake is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Flat Lake is safe to swim in today is a call for the Indiana Department of Environmental Management and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Flat Lake
These are the measurements IDEM publishes for Flat 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 367.8 µg/L. Chlorophyll-a 40.7 µg/L.
| 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 | 368µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 40.7µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
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Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
57 acres
Shoreline
2.3 mi
No bathymetric survey has been published for Flat Lake, so its depth is not documented here.
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EPA Impairment Status
Flat 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: Recreation.
Source: EPA ATTAINS assessment unit INK01P1075_00 · Official waterbody report
Nearby Lakes in Marshall County
Frequently asked questions about Flat Lake
Where is Flat Lake?
- Flat Lake is a lake in Marshall County, Indiana. Its water-quality measurements are published by IDEM and shown on this page as reported.
What is the water quality of Flat Lake?
- Flat Lake in Marshall County, Indiana has water-quality measurements published by IDEM, shown here as reported. Phosphorus: 367.8 µg/L. Chlorophyll-a (algae): 40.7 µg/L. Surface area: 57 acres.
Is Flat Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Flat Lake is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
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Where this data comes from
Measurements for Flat Lake come from the EPA Water Quality Portal. Per-sample source details are not recorded for this lake.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database