Updated Aug 2026
California Lake Water Quality
Water quality grades for 117 monitored lakes across 29 counties.
117 California lakes carry a grade. Most of the input data flows through monitoring run by the California State Water Resources Control Board, which feeds state, federal, and volunteer measurements into the EPA Water Quality Portal. A-grade lakes are scarce in California: about 5% of the dataset. Most lakes here sit in C or D — productive, often shallow, frequently algal in late summer.
The state's lakes lean eutrophic: enough nutrient input to support an active algal community, with the trade-offs in clarity and dissolved oxygen that come with it. San Joaquin ranks highest on average county grade (A). Marin sits lowest. With only 29 counties in the state, the cross-county spread is narrower than the within-county spread for most lakes.
Grade Distribution
All 117 California lakes in the index: 43 (36.8%) carry an A–F grade and 74 (63.2%) are not rated — their monitoring record does not meet the evidence bar.
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Top-Graded California Lakes
The highest water-quality grades in California — clarity, depth, and A-F grade at a glance.
Lake Map
California reports, fishing & travel
California Fishing & Recreation
Licenses, regulations, records, and where to fish across California.
Counties
All 29 California counties, ranked by average lake water quality. Compare them against every county nationwide in the county rankings, browse the full directory of graded lakes, or pick a different state.
Top 25 Cleanest Lakes
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity | Trophic | Access |
|---|---|---|---|---|---|---|
| 1 | AGlenhaven Lake | Lake | A | No recent samples | Mesotrophic | Not recorded |
| 2 | ALake Almanor | Plumas | A | No recent samples | Oligotrophic | Not recorded |
| 3 | ALake Oroville | Butte | A | No recent samples | Oligotrophic | Not recorded |
| 4 | ARumsey Slough by the Old Bridge Lake | Lake | A | No recent samples | Mesotrophic | Not recorded |
| 5 | ASherman Lake | Sacramento | A | No recent samples | Mesotrophic | Not recorded |
| 6 | AStaten Island Lake | San Joaquin | A | No recent samples | Mesotrophic | Not recorded |
| 7 | CBack Water Pond | Imperial | C | No recent samples | Eutrophic | Not recorded |
| 8 | CBuckingham Point Lake | Lake | C | No recent samples | Eutrophic | Not recorded |
| 9 | CFishing Point Lake | Lake | C | 1.6 ft | Eutrophic | Not recorded |
| 10 | CRumsey Slough Mouth Lake | Lake | C | 1.6 ft | Eutrophic | Not recorded |
| 11 | CWest Corner of Big Valley Rancheria Marina Lake | Lake | C | 2.1 ft | Eutrophic | Not recorded |
| 12 | DA Bridge Within the Oaks Keys on Blue Heron Drive Lake | Lake | D | No recent samples | Eutrophic | Not recorded |
| 13 | DAt End of El-Em St. on Elem Indian Colony Lake | Lake | D | No recent samples | Eutrophic | Not recorded |
| 14 | DBoat Ramp of Big Valley Rancheria Marina Lake | Lake | D | 2.2 ft | Eutrophic | Not recorded |
| 15 | DClear Lake A Mooring la | Lake | D | No recent samples | Eutrophic | Not recorded |
| 16 | DClear Lake A Mooring Oa | Lake | D | No recent samples | Eutrophic | Not recorded |
| 17 | DClear Lake A Mooring Ua | Lake | D | No recent samples | Eutrophic | Not recorded |
| 18 | DClear Lake Oaks | Lake | D | No recent samples | Eutrophic | Not recorded |
| 19 | DCopper Canyon Bay Lake | San Bernardino | D | 13.2 ft | Eutrophic | Not recorded |
| 20 | DCopper Canyon Inlet Lake | San Bernardino | D | 15.5 ft | Eutrophic | Not recorded |
| 21 | DCounty Park Lake | Lake | D | No recent samples | Eutrophic | Not recorded |
| 22 | DEast Corner of Big Valley Rancheria Marina Lake | Lake | D | 2 ft | Eutrophic | Not recorded |
| 23 | DElizabeth Lake | Los Angeles | D | No recent samples | Eutrophic | Not recorded |
| 24 | DHorseshoe Bend Lake | Lake | D | No recent samples | Eutrophic | Not recorded |
| 25 | DJackie'S Cove Lake | San Bernardino | D | 7.8 ft | Eutrophic | Not recorded |
25 Lakes Needing Attention
25 lakes25 graded lakes
| # | Lake | County | Grade | Clarity |
|---|---|---|---|---|
| 1 | FRodeo Lagoon E Top Lake | Marin | F | No recent samples |
| 2 | FRodeo Lagoon E Bottom Lake | Marin | F | No recent samples |
| 3 | FLake Shore Adjacent To New Tnt Restaurant on Shoreline | Lake | F | No recent samples |
| 4 | DWestern Boundary Lake | Lake | D | 1.5 ft |
| 5 | DTule Boat Launch Lake | Lake | D | 2.3 ft |
| 6 | DSolar Bee of Big Valley Rancheria Marina Lake | Lake | D | 2.3 ft |
| 7 | DShady Acres Campground Now Called Clearlake Campground | Lake | D | No recent samples |
| 8 | DRodman Slough Lake | Lake | D | No recent samples |
| 9 | DRodeo Lagoon W Bottom Lake | Marin | D | No recent samples |
| 10 | DRed Lake | Tuolumne | D | No recent samples |
| 11 | DRed Lake | Alpine | D | No recent samples |
| 12 | DPond | Del Norte | D | No recent samples |
| 13 | DOld Lakeport Tnt Restaurant | Lake | D | No recent samples |
| 14 | DMarina Lake Site | Lake | D | 2 ft |
| 15 | DLand'S End Slough Lake | Lake | D | 1.5 ft |
| 16 | DLake Morongo | Riverside | D | No recent samples |
| 17 | DLake Havasu Center | San Bernardino | D | 12.3 ft |
| 18 | DJago Bay Lake | Lake | D | No recent samples |
| 19 | DJackie'S Cove Lake | San Bernardino | D | 7.8 ft |
| 20 | DHorseshoe Bend Lake | Lake | D | No recent samples |
| 21 | DElizabeth Lake | Los Angeles | D | No recent samples |
| 22 | DEast Corner of Big Valley Rancheria Marina Lake | Lake | D | 2 ft |
| 23 | DCounty Park Lake | Lake | D | No recent samples |
| 24 | DCopper Canyon Inlet Lake | San Bernardino | D | 15.5 ft |
| 25 | DCopper Canyon Bay Lake | San Bernardino | D | 13.2 ft |
Lake Match
Which lake suits how you actually use one?
Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Source: EPA National Aquatic Resource Surveys and the EPA Water Quality Portal.