Clearest lakes in Minnesota

The clearest lakes

By measured Secchi depth, the clearest lake in Minnesota is Mahnomen, Alstead & Arco Mine in Crow Wing County, where readings average 32.3 ft across 5 readings from 2010 to 2022. Next come Caribou Lake in Itasca County (30.8 ft), Clearwater Lake in Cook County (27.3 ft) and Mountain Lake in Cook County (25.8 ft). The DNR map classes Mahnomen, Alstead & Arco Mine as a mine-pit lake, not a lake or pond. The clearest lake in the map’s lake-or-pond class is Caribou Lake.

Secchi depth is how far down a white disk stays visible. Every figure here is a measured reading, not a satellite estimate. A lake is ranked when it has at least 5 readings, taken in at least three different years, one of them 2016 or later, and covers 10 acres or more: 466 lakes pass. Each lake’s figure is the average of all its readings, the same figure its lake page on this site prints.

Minnesota Pollution Control Agency and volunteer Secchi readings, via Minnesota DNR LakeFinder, fetched 26 Oct 2026. Lakes of 10 acres or more with 5 or more readings in 3 or more years.

The top 25

The 25 clearest, in order. Under each name, the years of its first and latest reading. “Reads” is how many Secchi readings LakeFinder holds for the lake; “Range” runs from its murkiest reading to its clearest, in feet. The 25th lake averages 17.9 ft. Mountain Lake, Knife Lake and Ottertrack Lake cross the state line; the readings are the ones on Minnesota’s record. 6 of the 25 have a lake page on this site, linked by name.

Minnesota Pollution Control Agency and volunteer Secchi readings, via Minnesota DNR LakeFinder, fetched 26 Oct 2026.

Clearest is not cleanest

People search for the cleanest lakes as often as the clearest. These records answer only the second question. A Secchi reading measures how far you can see into the water. It is not a test for bacteria such as E. coli, for algae toxins, or for anything in the fish, and a lake with a high average can still have a murky week.

Minnesota publishes no statewide record of algal bloom reports, so this guide cannot rank lakes by blooms, and none of these readings says whether a lake is safe to swim in today. For a beach, the local health department or the beach’s owner posts closures; this site does not cover them yet.

What the readings can tell you is how clear a lake has been, over how many years, and how much it varies: Mahnomen, Alstead & Arco Mine has read between 25 and 38 ft.

Minnesota Pollution Control Agency and volunteer Secchi readings, via Minnesota DNR LakeFinder, fetched 26 Oct 2026. Algae: our How we measure page, Minnesota section (How we measure).

How many readings

LakeFinder holds Secchi readings for 2,451 Minnesota lakes of 10 acres or more, but most have very few: 661 have a single reading, the middle lake has 3, 476 have 5 or more and 94 have 10 or more. Mille Lacs Lake has the most, 924. One reading is one day, so lakes with fewer than 5 are not ranked.

42 lakes with three or four readings average clearer than the 25th lake on the list. The clearest named ones are Portsmouth Mine (Crow Wing County, 30.5 ft over 3 readings), South Lake (Cook County, 26.2 ft over 3 readings), Spider Lake (Hubbard County, 26.1 ft over 3 readings), Christmas Lake (Hennepin County, 26.0 ft over 3 readings) and Sagamore Mine (Crow Wing County, 25.7 ft over 3 readings). A few more readings could put them on the list or take them off it.

Counting only the 92 ranked lakes with 10 or more readings, the clearest are Clearwater Lake (27.3 ft over 10), Echo Lake (20.6 ft over 18), Trout Lake (18.6 ft over 35), Burntside Lake (18.1 ft over 26) and Thunder Lake (17.5 ft over 10).

Minnesota Pollution Control Agency and volunteer Secchi readings, via Minnesota DNR LakeFinder, fetched 26 Oct 2026.

When the readings were taken

Readings are taken when a monitor goes out, not on a schedule shared by every lake. Across the 25 lakes above, 94% of the readings fall in June to September. The lake whose summer readings differ most from its all-season average is Echo Lake: 22.1 ft from June to September against 20.6 ft over all its readings. 15 of the 25 have a reading from 2024 or 2025.

Where a lake has at least five readings before 2016 and five since, the two can differ. The widest gap among the 25 is Burntside Lake: 20.6 ft before 2016 and 13.3 ft since, on 17 and 9 readings. That is a difference between two small sets of days, not a measured trend.

Minnesota Pollution Control Agency and volunteer Secchi readings, via Minnesota DNR LakeFinder, fetched 26 Oct 2026.

Where the clear lakes are

The 466 ranked lakes lie in 54 counties. Cook County has the most, 84, then Lake (34), Cass (33) and Crow Wing (27). Half of the 466 average 9.1 ft or more; 10 average 20 ft or more and 73 average 15 ft or more. The least clear of the ranked lakes is Talcot Lake, at 0.6 ft.

Minnesota Pollution Control Agency and volunteer Secchi readings, via Minnesota DNR LakeFinder, fetched 26 Oct 2026. Counties as the DNR lists each lake.

What the figure is

A Secchi disk is a white disk lowered on a line until it disappears; that depth is the reading. The readings here are the ones Minnesota DNR’s LakeFinder carries for each lake, recorded by the Minnesota Pollution Control Agency and volunteer monitors. A lake the DNR maps in basins takes every basin’s readings, as its lake page does. Lakes are counted by the rule of our Minnesota lake count: the DNR map’s lake, reservoir and mine-pit classes, 10 acres or more.

How we read every kind of figure is on How we measure. Our Minnesota lake pages are listed on the Minnesota page.

Minnesota Pollution Control Agency and volunteer Secchi readings, via Minnesota DNR LakeFinder, fetched 26 Oct 2026. Lake classes and acres: Minnesota Department of Natural Resources, hydrography (lake, pond, reservoir and mine-pit lake classes), via the Metropolitan Council’s data mirror. Fetched 26 Oct 2026. Minnesota DNR data used under the DNR General Data and Software License. Not for navigation.