Updated August 2026
The State of Indiana's Lakes 2026
Of 22 lakes in Indiana, 50% earn a water-quality grade of A or B and 0% score D or F (average grade B). 15 lakes (68.2%) are on an official impaired-waters list.
Data Report
22
Monitored lakes graded
B
Average grade
50%
Grade A or B
68.2%
On impaired list
Indiana grade distribution
B
C
A: 0 (0.0%)B: 1 (50.0%)C: 1 (50.0%)D: 0 (0.0%)F: 0 (0.0%)
Cleanest lakes in Indiana
Highest combined water-quality score, 2026.
No qualifying lakes with sufficient data.
Most-polluted lakes
Lowest combined water-quality score among monitored lakes.
No qualifying lakes with sufficient data.
Worst algae hotspots
Highest measured chlorophyll-a (algae) concentration.
No qualifying lakes with sufficient data.
Trending lakes
Improving
- 1.NRWinona Lake — Kosciusko County
- 2.NRYellow Creek Lake — Kosciusko County
- 3.NRBig Chapman Lake — Kosciusko County
- 4.NRSyracuse Lake — Kosciusko County
Declining
- 1.NRLost Lake — Marshall County
- 2.NRLake George — Steuben County
- 3.NRKoontz Lake — Starke County
- 4.NRBeaver Dam Lake — Kosciusko County
- 5.NROswego Lake — Kosciusko County
- 6.NRLamb Lake — Johnson County
- 7.NRBig Barbee Lake — Kosciusko County
- 8.NRLake Lemon — Monroe County
Impaired waters in Indiana
15 lakes appear on the EPA/state 303(d) impaired-waters list (15 formally listed, 0 with a cleanup plan/TMDL).
Nutrients (phosphorus, nitrogen) · 8PCBs · 5Impaired biota (cause unknown) · 3
Explore Indiana lakes
Grades combine total phosphorus, total nitrogen, chlorophyll-a, and turbidity from the EPA Water Quality Portal and state agencies. See the full methodology, the national State of America’s Lakes report, or all Indiana lakes.
Cite this report: LakeQuality, “The State of Indiana's Lakes 2026”.