Lake Water Quality Answers
Direct answers to the questions people most often ask about Minnesota and Wisconsin lakes. Each answer pulls from EPA water quality data, Metropolitan Council grading methodology, and DNR fish surveys. Drill into a specific lake, a state, a county, or a general topic.
By State
Cleanest Lakes by County
Top 32 highest-lake-count counties shown. See all 607 counties →
Minnesota
- Cleanest lakes in St. Louis County(187 lakes)
- Cleanest lakes in Lake County(142 lakes)
- Cleanest lakes in Itasca County(141 lakes)
- Cleanest lakes in Cass County(132 lakes)
- Cleanest lakes in Cook County(128 lakes)
- Cleanest lakes in Crow Wing County(120 lakes)
- Cleanest lakes in Otter Tail County(97 lakes)
- Cleanest lakes in Hennepin County(95 lakes)
- Cleanest lakes in Becker County(93 lakes)
- Cleanest lakes in Beltrami County(92 lakes)
- Cleanest lakes in Hubbard County(76 lakes)
- Cleanest lakes in Wright County(64 lakes)
- Cleanest lakes in Stearns County(55 lakes)
- Cleanest lakes in Aitkin County(53 lakes)
- Cleanest lakes in Douglas County(51 lakes)
- Cleanest lakes in Ramsey County(49 lakes)
Wisconsin
- Cleanest lakes in Vilas County(191 lakes)
- Cleanest lakes in Oneida County(134 lakes)
- Cleanest lakes in Polk County(73 lakes)
- Cleanest lakes in Oconto County(62 lakes)
- Cleanest lakes in Burnett County(57 lakes)
- Cleanest lakes in Bayfield County(52 lakes)
- Cleanest lakes in Sawyer County(50 lakes)
- Cleanest lakes in Washburn County(47 lakes)
- Cleanest lakes in Waukesha County(45 lakes)
- Cleanest lakes in Douglas County(40 lakes)
- Cleanest lakes in Florence County(39 lakes)
- Cleanest lakes in Barron County(37 lakes)
- Cleanest lakes in Forest County(34 lakes)
- Cleanest lakes in Walworth County(34 lakes)
- Cleanest lakes in Iron County(33 lakes)
- Cleanest lakes in Langlade County(32 lakes)
Topics & Definitions
What causes algae bloomsWhat is blue green algaeAre lakes safe to swim inHow to tell if a lake is cleanWhat is a good secchi depthWhat is the deepest lake in mnWhat is the deepest lake in wiWhat is the largest lake in mnWhat is the largest lake in wiHow many lakes in mnHow many lakes in wiAre mn lakes cleaner than wiAre lakes safe for dogsWhat is eutrophicationWhy are some lakes green
Lake-Specific Answers
Every 1,000 answerable lake has three dedicated Q&A pages: swim safety, cleanliness, and (where data exists) fish species. Featured lakes below — search the full set on any lake page or the search page.