Deepest Lakes in America and How Clean They Are

2,051 measured lakes across the United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs. carry a rankable max-depth reading. 75 reach 100 feet or more; 6 clear 200 feet. Here are the 20 deepest fully measured lakes — with water-quality readings beside the depth, because a deep lake is not automatically a clean one.

The 20 deepest lakes in the measured dataset

Green Lake is the deepest lake we currently rank at 236 ft. The question this table answers is narrower than a list of the country’s deepest lakes: among lakes with nutrient and algae readings on record, which are the deepest, and is that deep water also clean? Lakes without a readine are left out, so every row carries both numbers.

Rank	Lake	State	Max depth	Clarity (ft)	Area
1	Green Lake	WI	236 ft	13.5	7,920 acres
2	Lasalle Lake	MN	213 ft	6.9	238 acres
3	Ten Mile Lake	MN	208 ft	20.5	5,080 acres
4	Loon Lake	MN	202 ft	17.4	1,095 acres
5	Gunflint Lake	MN	200 ft	16.5	4,009 acres
6	Larson Lake	MN	177 ft	21	208 acres
7	Carlos Lake	MN	163 ft	18	2,605 acres
8	Trout Lake	MN	157 ft	18	1,743 acres
9	Snowbank Lake	MN	150 ft	15.1	4,655 acres
10	Steamboat Bay Lake	MN	150 ft	9.8	103,444 acres
11	Six Lake	MN	140 ft	21	197 acres
12	Elmo Lake	MN	140 ft	11.1	257 acres
13	Whitefish Lake	MN	138 ft	14.4	7,714 acres
14	Long Lake	MN	135 ft	11.2	1,926 acres
15	Big Sand Lake	MN	135 ft	23	1,639 acres
16	Geneva Lake	WI	135 ft	21	5,401 acres
17	Kabekona Lake	MN	133 ft	12.1	2,433 acres
18	Koronis Lake	MN	132 ft	6	2,968 acres
19	Roosevelt Lake	MN	129 ft	11.1	1,511 acres
20	Long Lake	MN	128 ft	12.3	1,289 acres

Depth rankings for individual states are on the deepest-lakes ranking. For the statistical relationship between depth and nutrient readings across every lake with both fields, see Do Deeper Lakes Have Better Water Quality?.

Depth helps — it does not decide

Of these twenty deepest lakes, 19 sit in EPA's favourable classes. Their mean nutrient and algae reading is 3.80 versus 2.28 across all measured lakes — deeper water does lean cleaner on average. The mechanism is physical: deep lakes store cold water, limit summer algae growth in the upper layer, and dilute phosphorus loads that would overwhelm a shallow basin of the same acreage. The exception proves the rule — a deep reservoir receiving farm or urban runoff can still bloom at the surface while the hypolimnion stays cold and dark.

Cold, clear, and deep usually travel together in forested northern and mountain watersheds.
Deep + farmed watershed can still produce green surface water and mid-range readings.
Shallow + protected watershed can read cleaner than a deeper, greener lake, which is why both depth and the readings are published, never depth alone as a proxy for safety.

Depth records versus a lake you would actually swim in

Lists of the deepest lakes in the country are geography — Crater Lake, Tahoe, Chelan, the Great Lakes soundings — and they answer a trivia question rather than a trip-planning one. What they rarely include is whether that deep water is clear or clean. The table above pairs the depth with the grade for exactly that reason: a cabin buyer or a paddler wants to know if the deep lake is also the healthy one, and it often is, but not always.

If you are choosing a lake for swimming rather than bragging rights, start with the best swimming lakes and the cleanest lakes ranking, then use depth as a tie-breaker for cold-water clarity and summer comfort.

Frequently Asked Questions

Crater Lake in Oregon is the deepest lake in the U.S. at about 1,943 feet. This article ranks the deepest lakes inside the LakeQuality measured dataset — lakes with both a usable max-depth attribute and water-quality monitoring — which is a different and smaller universe than every named lake in the country.

Usually, yes — on average. Deep basins stay colder, stratify in summer, and dilute nutrient loads better than shallow warm lakes. In our data the deepest cohort carries a higher share of low nutrient and algae readings than the full lake set, but depth is not a guarantee: a deep reservoir in a farmed watershed can still read poorly.

Maximum depth comes from state natural-resource agency lake records and the HydroLAKES global lake database. Depths that contradict other measurements for the same lake, or that a survey has flagged as unreliable, are left out of the ranking rather than published as fact.

Depth itself is not a swim hazard the way cold shock and sudden drop-offs can be. Many deep, clear lakes are excellent for swimming near shore. Check the lake’s readings and current advisories, and respect cold-water safety even in midsummer.

The 20 deepest lakes in the measured dataset

Depth helps — it does not decide

Depth records versus a lake you would actually swim in

Frequently Asked Questions

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