Contra Costa County Lake Quality
California, 8 lakes — no lake here has enough monitoring data for a grade
Only 8 lakes in Contra Costa County carry an active grade. The county-level summary is therefore representative of those specific lakes, not necessarily of every water body in the county.
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. Contra Loma Reservoir (—) is the cleanest in the county.
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Quick Answers for Contra Costa County
Planning a trip? Check special fishing regulations for Contra Loma Reservoir — or check the official California fishing regulations.
All Lakes in Contra Costa County
8 lakes · 0 graded, 8 not rated0 graded lakes · 8 not rated, hidden
| # | Lake | Grade | Clarity | Phosphorus | Algae | Trophic | Access |
|---|---|---|---|---|---|---|---|
| NRContra Loma ReservoirContra Costa | NR | 4.1 ft | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRHolland Tract Middle PondContra Costa | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRHolland Tract North PondContra Costa | NR | No recent samples | No recent samples | 103.5 µg/L | No recent samples | Not recorded | |
| NRHolland Tract South PondContra Costa | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRLake AnzaContra Costa | NR | 12.3 ft | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRWebb Tract East PondContra Costa | NR | No recent samples | No recent samples | 88.3 µg/L | No recent samples | Not recorded | |
| NRWebb Tract Middle PondContra Costa | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded | |
| NRWebb Tract North PondContra Costa | NR | No recent samples | No recent samples | No recent samples | No recent samples | Not recorded |
NR = not rated: the monitoring record does not meet the evidence bar for a grade. That is EPA Integrated Reporting Category 3 (insufficient information), not a failing grade. How grading works.
Lake Match
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Six questions — swimming, fishing, quiet, cabins, drive time — and a shortlist of graded lakes that fit, with the water quality behind each one.
Other Counties in California
See how Contra Costa County stacks up in the national county water-quality rankings, or browse the full directory of graded lakes across all 49 states and 2 Canadian provinces.
Source: EPA National Aquatic Resource Surveys, 2026.