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Updated August 2026 · Top 25 of 70 lakes with a Secchi reading

Clearest Lake in Colorado: Top 25 by Secchi Depth

Rampart Reservoir in El Paso County is the clearest lake in Colorado by Secchi depth, at 28.5 ft. Mapped and ranked below: the 25 clearest of 70 Colorado lakes with a Secchi reading. Secchi depth is clarity alone: phosphorus and chlorophyll-a are separate readings, so a clear lake can carry higher nutrient readings than a murkier one.

Map · 25 ranked lakesTap a pin for its lakeTap a pin for the lake's page

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Nutrient and algae readings on recordNo reading on record#1 in this rankingPins are this ranking's lakes at their surveyed locations.

How clear are Colorado's clearest lakes?

From 28.5 ft at Rampart Reservoir to 8 ft at #25, Sweetwater Lake; the median of the 25 is 13.1 ft.

#	Lake	County	Secchi depth	Area
1	Rampart Reservoir	El Paso	28.5 ft	300 acres
2	Standley Lake	Jefferson	20.5 ft	1,222 acres
3	Lake Nighthorse	La Plata	18.7 ft	1,548 acres
4	Island Lake	Delta	16.7 ft	161 acres
5	Turquoise Reservoir	Lake	16.1 ft	1,788 acres
6	Crystal Reservoir	Montrose	15.4 ft	301 acres
7	Antero Reservoir	Park	14.8 ft	3,446 acres
8	Mountain Home Reservoir	Costilla	14.4 ft	597 acres
9	Pearl Lake	Routt	14.1 ft	166 acres
10	Twin Lakes East	Lake	14.1 ft	—
11	Haviland Lake	La Plata	13.8 ft	61 acres
12	Lake John	Jackson	13.8 ft	612 acres
13	Elevenmile Reservoir	Park	13.1 ft	—
14	Skaguay Reservoir	Teller	12.5 ft	88 acres
15	Summit Lake	Jackson	12.1 ft	—
16	Dillon Reservoir	Summit	11.6 ft	3,300 acres
17	Blue Mesa Reservoir	Gunnison	11.5 ft	—
18	Twin Lakes West	Lake	11.5 ft	—
19	Green Mountain Reservoir	Summit	11.5 ft	2,125 acres
20	Mcphee Reservoir	Montezuma	10.5 ft	4,918 acres
21	Ridgway Reservoir	Ouray	9.8 ft	1,109 acres
22	Grand Lake	Grand	8.7 ft	—
23	Dowdy Lake	Larimer	8.2 ft	83 acres
24	North Delaney Lake	Jackson	8.2 ft	258 acres
25	Sweetwater Lake	Garfield	8 ft	—

Sources and method

Secchi depth: Median of each lake's EPA Water Quality Portal readings, sampled January 2020 to September 2025, in feet. For 20 of these 25 lakes the submitting agency is Colorado Dept. of Public Health & Environment-WQCD. Portal: EPA Water Quality Portal.
Readings: clarity, phosphorus and chlorophyll-a from the agency's own sampling, shown as reported. Clarity is a separate measurement from nutrients and algae, which is why a clear lake here can carry higher phosphorus than a murkier one.
Area: state agency lake surveys and, for reservoirs, US Army Corps of Engineers National Inventory of Dams records, in acres at normal pool. A dash means no record carries one.
Map pins: all 25 table rows. No other lakes are plotted.

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Frequently Asked Questions

What is the clearest lake in Colorado?

Rampart Reservoir in El Paso County is the clearest lake in Colorado by Secchi depth, at 28.5 ft. Secchi depth is measured by lowering a black-and-white disk until it disappears from view; a deeper reading means clearer water. Rampart Reservoir’s phosphorus and chlorophyll-a readings are on its page.

How clear are Colorado's 25 clearest lakes?

They span 8 ft to 28.5 ft of Secchi depth, with a median of 13.1 ft. Rampart Reservoir leads by 8 ft. Jackson County has 3 of the 25; the rest are spread across 17 other counties.

How is water clarity measured?

Water clarity is measured by Secchi depth, named after the 19th-century Italian astronomer Pietro Angelo Secchi who developed the method. A standardized black-and-white disk is lowered into the water on a rope; the depth (in feet or meters) at which the disk disappears from view is recorded. Greater Secchi depth means clearer water, usually a sign of low sediment, low phosphorus, and limited algae growth. The figure for each lake here is the median of its readings.

What makes a lake clear?

Lake clarity is driven by three factors: low suspended sediment (clay, silt), low nutrient load (especially phosphorus, which fuels algae), and low chlorophyll-a (active algae biomass). Deep lakes with rocky basins and forested watersheds tend to be clearest because they take in little soil runoff and few nutrients. Shallow lakes in farmed watersheds are typically less clear because they receive more sediment and fertilizer runoff.

Is the clearest lake the cleanest?

Not always. Clarity (Secchi depth) is measured and shown; nutrient and algae readings (total phosphorus and chlorophyll-a) are a separate measurement, compared against that lake’s EPA ecoregion classes. A lake can be very clear but still have elevated phosphorus that just hasn't bloomed yet. See our companion cleanest-lakes ranking for Colorado for the nutrient-and-algae list.

Where to stay near Colorado's clearest lakes

Planning a trip? Jump to live cabin, resort, and hotel availability near Colorado's clearest lakes.

Clearest lakes across all states →Cleanest lakes in Colorado (combined score) →All Colorado lakes →

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