Contra Loma Reservoir
Contra Loma Reservoir in Contra Costa County, California is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 4.1 ft visibility. Surface area: 81 acres.
- Clarity
- 4.1 ft
- Area
- 81 acres
- Public access
- Yes
Why Contra Loma Reservoir has no grade
We grade a lake only when its monitoring record clears the evidence bar: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Contra Loma Reservoir, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). Sampling here has recorded water clarity, but not phosphorus and algae (chlorophyll-a).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by your state environmental agency and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Contra Loma Reservoir is a 81-acre lake in Contra Costa County, California. Limited fish-species data available. Public access is available with 1 public boat landing.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2023-07-27. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not ratedLimited data
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Contra Loma Reservoir
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Murky, only visible to about 4.1 ft. Trophic State Index: 57.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.1 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 57 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Contra Loma Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Contra Loma Reservoir in Contra Costa County, California — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
Top-rated places to stay near Contra Loma Reservoir
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 81 acres |
| Public Access | Yes |
No bathymetric survey has been published for Contra Loma Reservoir, so its depth is not documented here.
Recreation & Access
- Contra Loma Regional ParkPublic
Named access points from the USGS National Boat Ramps inventory, snapped within 5 km. More lakes with boat ramps
Fishing Contra Loma Reservoir
Reservoir Info (USACE NID)
Contra Loma Reservoir is a man-made reservoir impounded by the Contra Loma Dike 2 (completed 1967), built primarily for hydroelectric on the San Joaq River Os; earth-type dam, 25 ft tall and 360 ft long.
- Surface area
- 81 ac
- Normal storage
- 2,095 ac-ft
- Max storage
- 2,630 ac-ft
- Drainage area
- 1 sq mi
- Hazard class
- Low
- Owner
- BUREAU OF RECLAMATION
All listed purposes: Hydroelectric;Irrigation;Recreation.
Source: USACE National Inventory of Dams, NID ID CA10143 · Operator website
EPA Impairment Status
Contra Loma Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit CAL5440000020000217082907 · Official waterbody report
Graded lakes near Contra Loma Reservoir
Contra Loma Reservoir has no grade, but these lakes within a short drive do.
Nearby Lakes in Contra Costa County
Frequently asked questions about Contra Loma Reservoir
Where is Contra Loma Reservoir?
- Contra Loma Reservoir is a lake in Contra Costa County, California. LakeQuality has not rated this lake (UNRATED) — there is not enough recent sampling to assign a letter.
What is the water quality grade for Contra Loma Reservoir?
- Contra Loma Reservoir in Contra Costa County, California is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 4.1 ft visibility. Surface area: 81 acres.
Is Contra Loma Reservoir safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Contra Loma Reservoir is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
Are there boat ramps on Contra Loma Reservoir?
- Contra Loma Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Contra Loma Regional Park. Public access is listed as yes.
Explore Contra Loma Reservoir across LakeGrade
More California Lake Rankings
Other Lakes in California
Eutrophic Lakes in California
Where this data comes from
1 measurement from 1 monitoring station, 2023. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- North American Lake Management Society
NALMS1 sample · 2023
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Named boat-access points from the USGS National Boat Ramps inventory