Grand County, Colorado · Water Quality Report Card
Lake Granby Dam Bottom
Lake Granby Dam Bottom in Grand County, Colorado has a water quality grade of B (Good). Phosphorus: 13 µg/L.
- Mean depth
- ~76 ft est.
- Type
- Mesotrophic
- Trend
- ↑ Improving
Lake Granby Dam Bottom is a mesotrophic lake in Grand County, Colorado with an estimated average depth of about 76 feet. Water quality is graded B based on 2 sampling years through 2020. Overall water quality is improving over recent sampling years. Compared to the 6 other monitored lakes in Grand County, Lake Granby Dam Bottom ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, CDPHE, last sampled 2020-09-16. Grade methodology: LakeGrade methodology.
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Swimming Safety
Good for swimming, clear water with low algae levels
Water Quality Grade: B (Good)
No clarity data. Phosphorus level: 13 µg/L. Trophic State Index: 41.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No data | |
| Phosphorus | 13 µg/L | Good |
| Chlorophyll-a (Algae) | No data | |
| Trophic State Index (TSI) | 41 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Average Depth | ~76 ft est. |
Depth marked “est.” is a modeled estimate from HydroLAKES, not a measured survey. Colorado has not published bathymetry for Lake Granby Dam Bottom.
Where to stay near Lake Granby Dam Bottom
Compare lakeside cabins, hotels, and vacation rentals near Lake Granby Dam Bottom in Grand County, Colorado — 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.
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Fishing Lake Granby Dam Bottom
Water Quality Trend: ↑ Improving
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +44.08 m/yr | 4 |
| Phosphorus | ↓ Declining | +2.4 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -0.13 µg/L/yr | 3 |
Location
County Ranking
Ranked #2 of 7 lakes in Grand County
Cleaner Lakes Within 30 Miles
Lake Granby Dam Bottom holds Grade B. One nearby lake has a higher grade.
Nearby Lakes in Grand County
Explore Lake Granby Dam Bottom across LakeGrade
Planning a trip around Rocky Mountain?
Lake Granby Dam Bottom is about 17 miles from Rocky Mountain National Park. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Rocky Mountain →More Colorado Lake Rankings
Other Grade B Lakes in Colorado
Mesotrophic Lakes in Colorado
More records, surveys & data sources
Lake Size & Watershed
Size, shoreline, and watershed area from HydroLAKES (HydroSHEDS). Mean depth here is modelled, not surveyed — HydroLAKES v1.0 estimates lake depth from surrounding terrain rather than from soundings. Treat it as an approximation, and prefer a state bathymetric survey where one exists.
Where this data comes from
6 measurements from 1 monitoring station, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Colorado Dept. of Public Health & Environment-WQCD
21COL001_WQX6 samples · 2020
Analytical methods
- Phosphorus by Colorimetry
- Nitrogen in Water by Pyrolysis Detection
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
Lake size & watershed from HydroLAKES (HydroSHEDS)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion
Most recent sample: 2020-09-16
Monitoring stations: 1