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LakeQuality
Late afternoon sun over Slim Lake, scattering a bright path across wind-textured water

Boulder County Lake Quality

Colorado, 36 lakes, measured by Colorado WQCD

The county-level average smooths over real differences — a single agricultural watershed near the southwest corner can pull the average down even if the rest of the county runs clean. The 36 monitored lakes in Boulder County carry whatever clarity, phosphorus, and chlorophyll-a readings Colorado WQCD has published, shown as reported.

Most of the county's monitored lakes are shallow, under 50 feet, which means wind keeps the water column mixed all summer and sediment-bound phosphorus releases back into the surface layer whenever the bottom is disturbed.

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Where to stay near Boulder County

Top-rated places to stay near Boulder County

Prices for Oct 23–25, 4 adults. Change dates on the map below.

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Quick Answers for Boulder County

Cleanest lakes in Boulder County →Cleanest lakes in Colorado →Best swimming lakes in Colorado →

Planning a trip? Check special fishing regulations for N St Vrain Lake — or check the official Colorado fishing regulations.

All Lakes in Boulder County

36 lakes · 0 ranked on readings, 36 without enough sampling0 lakes ranked on readings · 36 without enough sampling, hidden

#LakeClarityPhosphorusAlgaeTrophicMax DepthAccess
N St Vrain LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Lake IsabelleBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Long LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Albion LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Goose LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Island LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Boulder ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Left Hand Valley ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Sixmile ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Hayden LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Leggett and Hillcrest ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Harper LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Base Line ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Marshall LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Waneka ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Barker ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Gross ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samples298.6 ftNot recorded
Gold LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Silver LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Left Hand ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Beaver ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Button Rock ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Allens LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Foothills ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Clover Basin ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
McIntosh LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Lagerman ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Dodd ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Gaynor LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Terry LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samples35 ftNot recorded
Crystal LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Walker ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Divide ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Ish ReservoirBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
Burch LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
McCall LakeBoulderNo recent samplesNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded

NR = no nutrient or algae reading on record. The measurements are published as the authority reports them. Where the data comes from.

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Other Counties in Colorado

Pueblo County

15 lakes

Jackson County

22 lakes

Montrose County

6 lakes

Moffat County

8 lakes

Jefferson County

29 lakes

San Juan County

8 lakes

Browse every Colorado lake, or the full directory of lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..

Source: the Water Quality Control Division of the Colorado Department of Public Health and Environment. See data sources.