Johnson Reservoir is a productive, nutrient-rich eutrophic lake in Sevier County, Utah. Water quality is graded D based on 2 sampling years through 2025. Compared to the 12 other monitored lakes in Sevier County, Johnson Reservoir ranks #11 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DNR, last sampled 2025-09-09. Grade methodology: LakeGrade methodology.
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Swimming Safety
Swimming not recommended, poor water quality with high algae risk
Water Quality Grade: D, Poor
Very murky, less than 2 ft of visibility. Chlorophyll-a: 29.1 µg/L. Trophic State Index: 66.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2 ft | F |
| Phosphorus | No data | |
| Chlorophyll-a (Algae) | 29.1 µg/L | D |
| Trophic State Index (TSI) | 66 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Where to stay near Johnson Reservoir
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Fishing Johnson Reservoir
Location
County Ranking
Ranked #11 of 13 lakes in Sevier County
Cleaner Lakes Within 30 Miles
Johnson Reservoir holds Grade D. 4 nearby lakes hold higher grades.
- ANla LakeSevier County · 5.9 mi · Two grade letters higher (D → A)
- AForsyth ReservoirSevier County · 8.4 mi · Two grade letters higher (D → A)
- DMill Meadow ReservoirWayne County · 8.2 mi · Higher overall water quality score
- DKoosharem ReservoirSevier County · 11.5 mi · Higher overall water quality score
Nearby Lakes in Sevier County
Explore Johnson Reservoir across LakeGrade
More Utah Lake Rankings
Other Grade D Lakes in Utah
Wayne County · Clarity: 5.9 ft
Piute County · Clarity: 1 ft
Garfield County · Clarity: 1.5 ft
Garfield County · Clarity: 5.7 ft
Garfield County · Clarity: 1.5 ft
Garfield County · Clarity: 6.1 ft
Eutrophic 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: 2025-09-09
Monitoring stations: 1