San Juan County, Colorado · Water Quality Report Card
Big Eldorado Lake
Big Eldorado Lake in San Juan County, Colorado is not rated for water quality — its monitoring record does not meet the evidence bar. Phosphorus: 3.5 µg/L.
- Type
- Oligotrophic
Big Eldorado Lake is a cold, clear oligotrophic lake in San Juan County, Colorado.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2020-09-21. Grade methodology: LakeGrade methodology.
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Swimming Safety
Not rated for swimming — there is not enough monitoring data to judge this lake
Water Quality Grade: Not rated
No clarity data. Phosphorus level: 3.5 µg/L. Trophic State Index: 22.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No data | |
| Phosphorus | 3.5 µg/L | |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 22 | Oligotrophic |
Low nutrients, clear water, excellent for swimming
Where to stay near Big Eldorado Lake
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Fishing Big Eldorado Lake
Location
Nearby Lakes in San Juan County
Explore Big Eldorado Lake across LakeGrade
3 documented falls within 23.5 mi, nearest Bridal Veil Falls
Species activity outlook by water temperature and season
Where to stay at Colorado's top lakes, each with its grade
Low nutrients, clear water, excellent for swimming
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More records, surveys & data sources
Where this data comes from
2 measurements from 1 monitoring station, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- USGS Colorado Water Science Center
USGS-CO2 samples · 2020
Analytical methods
- P, wu, WCA, persulfate CF color
Monitoring station identifiers (1)
Grade thresholds come from the U.S. EPA National Lakes Assessment 2022 Technical Support Document (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated.
Data Sources
Water quality data from the EPA Water Quality Portal
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion
Most recent sample: 2020-09-21
Monitoring stations: 1