
Updated August 2026
Lakes with Declining Water Quality
2,864 lakes across US lakes with nutrient and algae readings show declining water quality trends. These lakes have gotten worse based on multi-year monitoring of clarity, phosphorus, and algae levels.
| Rank | Lake | County | State | Trend | Years Monitored |
|---|---|---|---|---|---|
| 1 | Round Lake | Itasca | MN | ↓ Declining | 2 |
| 2 | Horseshoe Lake | Stearns | MN | ↓ Declining | 4 |
| 3 | Long Lake | Stearns | MN | ↓ Declining | 6 |
| 4 | Long Lake | Kandiyohi | MN | ↓ Declining | 4 |
| 5 | Long Lake | Hennepin | MN | ↓ Declining | 6 |
| 6 | Clear Lake | Meeker | MN | ↓ Declining | 6 |
| 7 | Clear Lake | Waseca | MN | ↓ Declining | 5 |
| 8 | Clear Lake | Jackson | MN | ↓ Declining | 2 |
| 9 | Eagle Lake | Hennepin | MN | ↓ Declining | 6 |
| 10 | Eagle Lake | Carver | MN | ↓ Declining | 6 |
| 11 | Fish Lake | Wright | MN | ↓ Declining | 6 |
| 12 | Washington Lake | Le Sueur | MN | ↓ Declining | 6 |
| 13 | East Solomon Lake | Kandiyohi | MN | ↓ Declining | 5 |
| 14 | Norway Lake | Kandiyohi | MN | ↓ Declining | 6 |
| 15 | East Auburn Lake | Carver | MN | ↓ Declining | 6 |
| 16 | Grace Lake | Carver | MN | ↓ Declining | 6 |
| 17 | Bass Lake | Hennepin | MN | ↓ Declining | 6 |
| 18 | Cedar Lake | Scott | MN | ↓ Declining | 4 |
| 19 | Wassermann Lake | Carver | MN | ↓ Declining | 6 |
| 20 | Thompson Lake | Dakota | MN | ↓ Declining | 2 |
| 21 | Sandy Lake | Anoka | MN | ↓ Declining | 5 |
| 22 | Jefferson Lake | Le Sueur | MN | ↓ Declining | 6 |
| 23 | Silver Lake | Ramsey | MN | ↓ Declining | 6 |
| 24 | Goose Lake | Ramsey | MN | ↓ Declining | 6 |
| 25 | Goose Lake | Hennepin | MN | ↓ Declining | 2 |
| 26 | Typo Lake | Anoka | MN | ↓ Declining | 6 |
| 27 | Rock Lake | Wright | MN | ↓ Declining | 2 |
| 28 | Como Lake | Ramsey | MN | ↓ Declining | 6 |
| 29 | Crystal Lake | Hennepin | MN | ↓ Declining | 5 |
| 30 | Crystal Lake | Blue Earth | MN | ↓ Declining | 4 |
| 31 | Ann Lake | Kanabec | MN | ↓ Declining | 6 |
| 32 | Knife Lake | Kanabec | MN | ↓ Declining | 6 |
| 33 | Mink Lake | Wright | MN | ↓ Declining | 6 |
| 34 | Red Rock Lake | Douglas | MN | ↓ Declining | 6 |
| 35 | Elk Lake | Sherburne | MN | ↓ Declining | 6 |
| 36 | Rush Lake | Sherburne | MN | ↓ Declining | 5 |
| 37 | Schultz Lake | Kandiyohi | MN | ↓ Declining | 6 |
| 38 | Alice Lake | Otter Tail | MN | ↓ Declining | 5 |
| 39 | Smith Lake | Douglas | MN | ↓ Declining | 6 |
| 40 | Wellner-Hageman Reservoir | Brown | MN | ↓ Declining | 4 |
| 41 | Vadnais Lake | Ramsey | MN | ↓ Declining | 6 |
| 42 | North Brown'S Lake | Stearns | MN | ↓ Declining | 6 |
| 43 | Martha Lake | Wright | MN | ↓ Declining | 6 |
| 44 | Caroline Lake | Wright | MN | ↓ Declining | 6 |
| 45 | Victoria Lake | Hennepin | MN | ↓ Declining | 2 |
| 46 | Gerhardt Lake | Dakota | MN | ↓ Declining | 6 |
| 47 | Cedar Island Lake | Stearns | MN | ↓ Declining | 4 |
| 48 | Sarah Lake | Hennepin | MN | ↓ Declining | 6 |
| 49 | Circle Lake | Rice | MN | ↓ Declining | 6 |
| 50 | Little Rock Lake | Benton | MN | ↓ Declining | 6 |
More on water-quality trends
Which lakes are actually improving: multi-year EPA monitoring trends, the named recoveries still in progress, and what it takes to move the readings.
The lakes with the steepest multi-year declines in clarity and the sharpest rises in nutrients, what is driving the drop, and which ones may recover.
A data snapshot of the lakes we track: the clearest and the greenest states, and where the water is improving.
How nutrient and algae readings are read against EPA ecoregion condition classes, what each class means in the water, and why a clean reading is not a clearance.
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