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

Elmore County Lake Quality

Idaho, 11 lakes — no lake here has enough monitoring data for a grade

Elmore County holds 11 monitored lakes. With a sample that small the county-level summary describes those specific waters, not necessarily every water body in the county. No lake in Elmore County has enough sampling behind it for an A–F grade yet. The 11 monitored lakes below carry whatever clarity, phosphorus, and chlorophyll-a measurements exist.

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 Elmore County

Top-rated places to stay near Elmore County

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Quick Answers for Elmore County

Cleanest lakes in Elmore County →Cleanest lakes in Idaho →Safest swimming lakes in Idaho →

Planning a trip? Check special fishing regulations for Arrowrock Reservoir — or check the official Idaho fishing regulations.

All Lakes in Elmore County

11 lakes · 0 graded, 11 not rated0 graded lakes · 11 not rated, hidden

#LakeGradeClarityPhosphorusAlgaeTrophicAccess
NRArrowrock ReservoirElmoreNR12.5 ft35 µg/L1.5 µg/LNo recent samplesNot recorded
NRCat Creek Reference LakeElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRCow Creek ReservoirElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBlair Trail ReservoirElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRMorrow ReservoirElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRLittle Camas ReservoirElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samples✓ Public
NRLong Tom ReservoirElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRUpper Teapot ReservoirElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRLower Teapot ReservoirElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRBig Trinity LakeElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded
NRSpangle LakeElmoreNRNo recent samplesNo recent samplesNo recent samplesNo recent samplesNot recorded

NR = not rated: there is not enough recent sampling to support a letter. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.

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Other Counties in Idaho

Gem County

2 lakes · Avg grade A

Canyon County

2 lakes · Avg grade A

Bear Lake County

3 lakes · Avg grade C

Valley County

26 lakes · Avg grade C

Bonneville County

9 lakes · Avg grade C

Blaine County

12 lakes · Avg grade D

See how Elmore County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all United States (49 states), Canada (Ontario, Québec, Nova Scotia, British Columbia and Newfoundland and Labrador), and 38 other country hubs..

Source: EPA National Aquatic Resource Surveys, 2026.