Lake San Marcos
Lake San Marcos in San Diego County, California is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 56 acres.
- Area
- 56 acres
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Why Lake San Marcos has no grade
We grade a lake only when the monitoring record supports a letter: 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 Lake San Marcos, no water-quality sampling on record for this lake.
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.
Lake San Marcos is a 56-acre lake in San Diego County, California.
Source: EPA Water Quality Portal sampling records, your state environmental agency, last sampled recent years. Grade methodology: LakeQuality methodology.
Watch Lake San Marcos water quality
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Swimming Safety
Not ratedElevated nutrients
Not rated for swimming — there is not enough monitoring data to judge this lake
Water quality measurements for Lake San Marcos
These readings exist but are not enough for an A–F grade — see why.
No clarity data. Trophic State Index: undefined.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) |
Where to stay near Lake San Marcos
Compare lakeside cabins, hotels, and vacation rentals near Lake San Marcos in San Diego 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 Lake San Marcos
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Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 56 acres |
No bathymetric survey has been published for Lake San Marcos, so its depth is not documented here.
Fishing Lake San Marcos
Nearby Lakes in San Diego County
Frequently asked questions about Lake San Marcos
Where is Lake San Marcos?
- Lake San Marcos is a lake in San Diego County, California. LakeQuality has not rated this lake (UNRATED) — no water-quality sampling on record for this lake.
What is the water quality grade for Lake San Marcos?
- Lake San Marcos in San Diego County, California is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 56 acres.
Is Lake San Marcos safe to swim in?
- Not rated for swimming — there is not enough monitoring data to judge this lake. Lake San Marcos is not rated for water quality — its monitoring record does not meet the evidence bar. Always check local health department advisories before swimming.
Explore Lake San Marcos across LakeQuality
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Where this data comes from
Measurements for Lake San Marcos come from the EPA Water Quality Portal. Per-sample source details are not recorded for this lake.