Gunlock Reservoir is a mesotrophic lake in Washington County, Utah. Water quality is graded B based on 2 sampling years through 2025. Compared to the 14 other monitored lakes in Washington County, Gunlock Reservoir ranks #10 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DNR, last sampled 2025-08-19. Grade methodology: LakeGrade methodology.
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Swimming Safety
Good for swimming, clear water with low algae levels
Water Quality Grade: B, Good
Murky, only visible to about 4.6 ft. Chlorophyll-a: 2.9 µg/L. Trophic State Index: 48.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 4.6 ft | D |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 2.9 µg/L | A |
| Trophic State Index (TSI) | 48 | Mesotrophic |
Moderate nutrients, good water quality
Where to stay near Gunlock Reservoir
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Fishing Gunlock Reservoir
Location
County Ranking
Ranked #10 of 15 lakes in Washington County
Cleaner Lakes Within 30 Miles
Gunlock Reservoir holds Grade B. One nearby lake has a higher grade.
See full comparison →Nearby Lakes in Washington County
Explore Gunlock Reservoir across LakeGrade
More Utah Lake Rankings
Other Grade B Lakes in Utah
Mesotrophic Lakes in Utah
More records, surveys & data sources
Data Sources
Water quality data from the EPA Water Quality Portal
Grading methodology based on Metropolitan Council standards
Most recent sample: 2025-08-19
Monitoring stations: 1