Contra Loma Reservoir
Contra Costa County, California81 acresView mapDirections
SWRCB publishes the water-quality measurements for Contra Loma Reservoir. Here is what has been measured.
- Impaired · Mercury
- Public access
- Limited data
Contra Loma Reservoir in Contra Costa County, California has water-quality measurements published by SWRCB, shown here as reported. Water clarity: 4.1 ft visibility. Surface area: 81 acres.
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. Methodology: how these readings are compared.
What Contra Loma Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Contra Loma Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
Whether Contra Loma Reservoir is safe to swim in today is a call for the California State Water Resources Control Board and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Contra Loma Reservoir
These are the measurements SWRCB publishes for Contra Loma Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 4.1 ft. TSI 57.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.1ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 57 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Contra Loma Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
81 acres
Public access
Yes
Listed by SWRCB
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 in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
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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
Designated uses not supporting: Fish consumption, Other.
Source: EPA ATTAINS assessment unit CAL5440000020000217082907 · Official waterbody report
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. Its water-quality measurements are published by SWRCB and shown on this page as reported.
What is the water quality of Contra Loma Reservoir?
- Contra Loma Reservoir in Contra Costa County, California has water-quality measurements published by SWRCB, shown here as reported. Water clarity: 4.1 ft visibility. Surface area: 81 acres.
Is Contra Loma Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Contra Loma Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for mercury. Check local advisories before you swim.
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.
Can I fish at Contra Loma Reservoir?
- Contra Loma Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by California's fish and wildlife agency, so check its current regulations before you go.
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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)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from 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