Best Lakes for Swimming
Not all lakes are created equal when it comes to swimming. Water quality varies dramatically, some lakes have crystal clear water with visibility exceeding 20 feet, while others are so murky you cannot see your hand below the surface. Here is how to use water quality data to find the best swimming lakes.
Looking for the best swimming lakes in a specific state? Jump straight to a state ranking of algae-safe, Grade A and B lakes: Minnesota · Wisconsin · Illinois · Michigan · Iowa · Ohio · Pennsylvania · New York · Missouri · Indiana · North Dakota · South Dakota
How to Read Lake Grades for Swimming
LakeQuality assigns every monitored lake a grade from A to F based on three metrics that directly affect swimming safety:
- Water Clarity (Secchi Depth), measured in feet. Higher is better. You want at least 4-5 feet of visibility to see underwater hazards. A-graded lakes have over 15 feet of visibility.
- Phosphorus, the nutrient that feeds algae. Lower is better. High phosphorus means more algae blooms, which can produce toxins harmful to humans and pets.
- Chlorophyll-a, directly measures algae in the water. Below 5 µg/L (grade A) means minimal algae. Above 20 µg/L means visible algae that may include harmful blue-green varieties.
Swimming Safety by Grade
| Grade | Swimming Assessment |
|---|---|
| A | Excellent, crystal clear water, minimal algae, ideal for swimming |
| B | Good, clear water, low algae, safe for swimming |
| C | Fair, moderate clarity, some algae may be present, generally safe |
| D | Poor, murky water, high algae risk, swimming not recommended |
| F | Avoid, very poor quality, potential algae toxins, do not swim |
Top 25 Lakes for Swimming
These lakes have the best water quality grades and are ideal for swimming and recreation:
| Rank | Lake | County | State | Grade | Clarity |
|---|---|---|---|---|---|
| 1 | East Fox Lake | Crow Wing | MN | A | 16.4 ft |
| 2 | North Long Lake | Crow Wing | MN | A | 15.1 ft |
| 3 | Bad Medicine Lake | Becker | MN | A | 25 ft |
| 4 | Big Sugar Bush Lake | Becker | MN | A | 16.5 ft |
| 5 | Round Lake | Cook | MN | A | 16.5 ft |
| 6 | Round Lake | Beltrami | MN | A | 18 ft |
| 7 | Horseshoe Lake | Cass | MN | A | 21 ft |
| 8 | Long Lake | Cass | MN | A | 21.5 ft |
| 9 | Long Lake | Clearwater | MN | A | 20.5 ft |
| 10 | Long Lake | Beltrami | MN | A | 20 ft |
| 11 | Long Lake | Becker | MN | A | 19.3 ft |
| 12 | Long Lake | Cass | MN | A | 17 ft |
| 13 | Long Lake | Itasca | MN | A | 16.7 ft |
| 14 | Long Lake | Itasca | MN | A | 16.9 ft |
| 15 | Dead Lake | Hubbard | MN | A | 16 ft |
| 16 | West Twin Lake | Crow Wing | MN | A | 20 ft |
| 17 | Sunshine Lake | St. Louis | MN | A | 20 ft |
| 18 | Otter Lake | Otter Tail | MN | A | 18 ft |
| 19 | Ossawinnamakee Lake | Crow Wing | MN | A | 20 ft |
| 20 | Clear Lake | Crow Wing | MN | A | 18 ft |
| 21 | Clear Lake | Aitkin | MN | A | 15 ft |
| 22 | Clear Lake | Itasca | MN | A | 14.9 ft |
| 23 | Eagle Lake | Otter Tail | MN | A | 22.6 ft |
| 24 | West Fox Lake | Crow Wing | MN | A | 15 ft |
| 25 | Spearhead Lake | Hubbard | MN | A | 15 ft |
Blue-Green Algae Warning Signs
Even if a lake has a good historical grade, blue-green algae blooms can appear quickly during hot summer weather. Watch for these warning signs before entering the water:
- Water that looks like green paint or pea soup
- Floating green or blue-green mats on the surface
- A strong musty or earthy odor from the water
- Dead fish along the shoreline
- Signs posted by local health departments
If you see any of these signs, do not swim, wade, or let pets drink from the lake. Blue-green algae(cyanobacteria) can produce toxins that cause skin rashes, nausea, and in severe cases, liver damage.
Frequently Asked Questions
Is it safe to swim in Minnesota lakes?
Most Minnesota lakes are safe for swimming. Lakes graded A or B by LakeQuality have excellent to good water quality with clear water and low algae. Lakes graded D or F should be avoided due to high algae levels that may produce harmful toxins. Always check for local advisories before swimming.
How do I know if a lake has harmful algae?
Blue-green algae (cyanobacteria) blooms look like green paint, pea soup, or floating mats on the water surface. A high chlorophyll-a reading (above 20 µg/L) indicates significant algae. Lakes with a D or F grade for chlorophyll-a should be avoided for swimming.
What Secchi depth is safe for swimming?
A Secchi depth of 4 feet or more generally indicates water clear enough for safe swimming. Lakes with Secchi depth over 15 feet (grade A) are crystal clear. Murky water with less than 3 feet of visibility makes it hard to see underwater hazards.
Are Wisconsin lakes safe to swim in?
Many Wisconsin lakes offer excellent swimming. The clearest lakes in Wisconsin have visibility exceeding 10-15 feet. Check individual lake grades on LakeQuality, A and B rated lakes are excellent for swimming.
Which states does this swimming ranking cover?
The ranking spans every state LakeQuality covers, currently 12 states: Minnesota, Wisconsin, Illinois, Michigan, Iowa, Ohio, Pennsylvania, New York, Missouri, Indiana, North Dakota, and South Dakota. Any A- or B-graded lake in those states can appear in the top 25.