Lake San Marcos
San Diego County, California56 acresView mapDirections
No nutrient or algae sampling on record from SWRCB for this lake.
- Impaired · Ammonia
- Limited data
Lake San Marcos in San Diego County, California has water-quality measurements published by SWRCB, shown here as reported. Surface area: 56 acres.
Lake San Marcos is a 56-acre lake in San Diego County, California.
Source: EPA Water Quality Portal sampling records, your state environmental agency. Methodology: how these readings are compared.
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Lake San Marcos is listed impaired under Clean Water Act §303(d) (IR 5) for ammonia, metals (other than mercury), nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Lake San Marcos 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 Lake San Marcos
These are the measurements SWRCB publishes for Lake San Marcos, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data.
Ask about Lake San Marcos
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
56 acres
Shoreline
3.6 mi
No bathymetric survey has been published for Lake San Marcos, so its depth is not documented here.
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Stays near Lake San Marcos
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Fishing Lake San Marcos
EPA Impairment Status
Lake San Marcos 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: Aquatic life.
Source: EPA ATTAINS assessment unit CAL9045200019991117152408 · Official waterbody report
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. Its water-quality measurements are published by SWRCB and shown on this page as reported.
What is the water quality of Lake San Marcos?
- Lake San Marcos in San Diego County, California has water-quality measurements published by SWRCB, shown here as reported. Surface area: 56 acres.
Is Lake San Marcos safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Lake San Marcos is listed impaired under Clean Water Act §303(d) (IR 5) for ammonia, metals (other than mercury), nutrients (phosphorus, nitrogen). Check local advisories before you swim.
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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.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database