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LakeQuality

Data Report · Updated July 2026

The State of Indiana’s Lakes 2026

Of 22 monitored lakes in Indiana, 22.7% earn a water-quality grade of A or B and 54.5% score D or F (average grade D). Grand Calumet Lagoon Lake is the cleanest; 15 lakes (68.2%) are on an official impaired-waters list.

22
Monitored lakes graded
D
Average grade
22.7%
Grade A or B
68.2%
On impaired list

Indiana grade distribution

B
C
D
F
A: 1 (4.5%)B: 4 (18.2%)C: 5 (22.7%)D: 6 (27.3%)F: 6 (27.3%)

Cleanest lakes in Indiana

Highest combined water-quality score, 2026.

  1. 1.BGrand Calumet Lagoon Lake — Lake County39 µg/L P · 3 µg/L chl-a

Most-polluted lakes

Lowest combined water-quality score among monitored lakes.

  1. 1.BGrand Calumet Lagoon Lake — Lake County39 µg/L P · 3 µg/L chl-a

Worst algae hotspots

Highest measured chlorophyll-a (algae) concentration.

No qualifying lakes with sufficient data.

Trending lakes

Improving

  1. 1.CCenter Lake — Kosciusko County
  2. 2.CSyracuse Lake — Kosciusko County
  3. 3.DJames Lake — Kosciusko County
  4. 4.FYellow Creek Lake — Kosciusko County
  5. 5.FPike Lake — Kosciusko County

Declining

  1. 1.FBig Barbee Lake — Kosciusko County
  2. 2.FLake Lemon — Monroe County
  3. 3.DKoontz Lake — Starke County
  4. 4.DLake Wawasee — Kosciusko County
  5. 5.CLamb Lake — Johnson County
  6. 6.BLake George — Steuben County
  7. 7.BOswego Lake — Kosciusko 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

Grades combine Secchi clarity, total phosphorus, and chlorophyll-a 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,” lakequality.org/report/in.