Deepest Lakes in America We Grade — and How Clean They Are

1,966 graded lakes across the 36 states and 2 Canadian provinces carry a rankable max-depth reading. 75 reach 100 feet or more; 8 clear 200 feet. Here are the 20 deepest fully graded lakes — with water-quality grades beside the depth, because a deep lake is not automatically a clean one.

The 20 deepest lakes in the graded dataset

Green Lake is the deepest lake we currently rank at 236 ft, carrying an overall grade of A. This list will never replace Wikipedia’s “deepest lakes in the US” page — Crater Lake sits outside that comparison on purpose — but it answers the practical question travelers ask next: among lakes we fully grade for water quality, which are the deepest, and are they clean? Unrated deep pits are excluded so every row has both depth and a grade.

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

Live depth rankings by state sit at /ranking/deepest. For the statistical relationship between depth and grade 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 grade A or B. Their mean grade score is 3.80 versus 2.68 across all graded 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 a middling grade.
Shallow + protected watershed can out-grade a deeper, dirtier lake — which is why we publish both depth and quality, never depth alone as a proxy for safety.

How this compares to “deepest lakes in the US” listicles

Search for “deepest lakes in the US” and you get Wikipedia, History.com, and map-porn listicles built around Crater Lake, Lake Tahoe, Lake Chelan, and a handful of Great Lakes soundings. Those pages answer a geography quiz. They rarely attach water-quality grades, Secchi readings, or swim context. LakeQuality’s depth pages exist to do the second job: show depth and the grade so a cabin buyer or paddler can tell whether the deep water is also the clean water.

If you are choosing a lake for swimming rather than bragging rights, start with the best swimming lakes and the cleanest-and-dirtiest 2026 report, 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 graded 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 A and B grades than the full lake set, but depth is not a guarantee: a deep reservoir in a farmed watershed can still grade poorly.

Max depth comes from state DNR / lake-finder attributes and HydroLAKES morphometry joined into each lake record. We only rank lakes whose depth passes the site’s rankable-depth checks (contradictory or survey-flagged depths are excluded).

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 water-quality grade and current advisories, and respect cold-water safety even in midsummer.

The 20 deepest lakes in the graded dataset

Depth helps — it does not decide

How this compares to “deepest lakes in the US” listicles

Frequently Asked Questions

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