Don Castro Reservoir
Don Castro Reservoir in Alameda County, California is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 0.3 ft visibility. Surface area: 24 acres.
- Clarity
- 0.3 ft
- Area
- 24 acres
Why Don Castro 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 Don Castro 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.
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. 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 Don Castro Reservoir
These readings exist but do not meet the evidence bar for an A–F grade — see why.
Very murky, less than 0.3 ft of visibility. Trophic State Index: 93.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 0.3 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 93 | Hypereutrophic |
Very high nutrients, dense algae, poor clarity
Where to stay near Don Castro Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Don Castro Reservoir in Alameda 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 Don Castro Reservoir
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 24 acres |
No bathymetric survey has been published for Don Castro Reservoir, so its depth is not documented here.
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. LakeQuality has not rated this lake (UNRATED) — there is not enough recent sampling to assign a letter.
What is the water quality grade for Don Castro Reservoir?
- Don Castro Reservoir in Alameda County, California is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 0.3 ft visibility. Surface area: 24 acres.
Is Don Castro Reservoir safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Don Castro Reservoir is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
Explore Don Castro Reservoir across LakeGrade
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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)
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.