Don Castro Reservoir
Alameda County, California24 acresView mapDirections
SWRCB publishes the water-quality measurements for Don Castro Reservoir. Here is what has been measured.
- Limited data
Don Castro Reservoir in Alameda County, California has water-quality measurements published by SWRCB, shown here as reported. Water clarity: 0.3 ft visibility. Surface area: 24 acres.
Don Castro Reservoir is a 24-acre lake in Alameda County, California.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled 2022-07-28. Methodology: how these readings are compared.
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Don Castro 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 Don Castro Reservoir
These are the measurements SWRCB publishes for Don Castro Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Very murky, less than 0.3 ft of visibility. TSI 93.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 0.3ft | 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. | 93 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Don Castro Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
24 acres
No bathymetric survey has been published for Don Castro Reservoir, so its depth is not documented here.
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Fishing Don Castro Reservoir
Reservoir Info (USACE NID)
Don Castro Reservoir is a man-made reservoir impounded by the San Lorenzo Creek (completed 1964), built primarily for flood risk reduction on the San Lorenzo Creek; earth-type dam, 65 ft tall and 385 ft long.
- Surface area
- 24 ac
- Max storage
- 380 ac-ft
- Drainage area
- 19.9 sq mi
- Hazard class
- High
- Owner
- Alameda County Public Works Agency
All listed purposes: Flood Risk Reduction;Other;Recreation.
Source: USACE National Inventory of Dams, NID ID CA00841 · Operator website · Matched by proximity (0.38 km)
Nearby Lakes in Alameda County
Frequently asked questions about Don Castro Reservoir
Where is Don Castro Reservoir?
- Don Castro Reservoir is a lake in Alameda County, California. Its water-quality measurements are published by SWRCB and shown on this page as reported.
What is the water quality of Don Castro Reservoir?
- Don Castro Reservoir in Alameda County, California has water-quality measurements published by SWRCB, shown here as reported. Water clarity: 0.3 ft visibility. Surface area: 24 acres.
Is Don Castro Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
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Where this data comes from
2 measurements from 1 monitoring station, 2022. Retrieved from the EPA Water Quality Portal on 2026-08-21.
Collected and reported by
- North American Lake Management Society
NALMS2 samples · 2022
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.