Johnson Reservoir
Sevier County, UtahView mapDirections
Nutrients and algae run above the regional average.
- Eutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- #5 of 7 in the county
- 17 ft max depth
- Public access
- Limited data
Johnson Reservoir in Sevier County, Utah has a water quality grade of D (Nutrient-rich). Water clarity: 2 ft visibility. Phosphorus: 82 µg/L. Chlorophyll-a (algae): 29.1 µg/L.
- Clarity
- 2 ft
- Max depth
- ~17 ft est.
- Type
- Eutrophic
- Phosphorus
- 82 µg/L
- Chlorophyll-a
- 29.1 µg/L
- Trend
- → Stable
- Public access
- Yes
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Stays near Johnson Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Johnson Reservoir in Sevier County, Utah — 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. The water-quality grade measures nutrients and algae, not lodging — cabins and rentals around Johnson Reservoir are listed below.
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Johnson Reservoir is a productive, nutrient-rich eutrophic lake in Sevier County, Utah with an estimated average depth of about 17 feet. Water quality is graded D based on 2 sampling years through 2025. Water clarity is declining over recent sampling years. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 6 other monitored lakes in Sevier County, Johnson Reservoir ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2025-09-09. Grade methodology: LakeQuality methodology.
What Johnson Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
- Camping3 public campgrounds nearby
Swimming Safety
Grade onlyLimited data
Based on clarity and algae grades from past sampling — we do not hold live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
The D is nutrients and algae, not a swimming clearance. Johnson Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Water Quality Grade: D (Nutrient-rich)
Very murky, less than 2 ft of visibility. Phosphorus 82 µg/L. Chlorophyll-a 29.1 µg/L. TSI 66. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2 ft | Not graded |
| Phosphorus | 82 µg/L | Poor |
| Chlorophyll-a (Algae) | 29.1 µg/L | Poor |
| Trophic State Index (TSI) | 66 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~17 ft est. |
| Public Access | Yes |
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Utah has not published bathymetry for Johnson Reservoir.
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.
Recreation & Access
- Johnson ReservoirPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Public campgrounds near Johnson Reservoir
- Paiute Campground1.8 km
- Tasha Equestrian Campground2.3 km
- Frying Pan Campground3.6 km
Nearest public campgrounds in the USGS National Map inventory, within about 3 miles. An empty list means USGS records no campground that close, which is not the same as camping being unavailable. Where the source gives an official reservation link, it is used; the cabin and hotel search does not cover campsites. More camping lakes
Fishing Johnson Reservoir
Water Quality Trend: → Stable
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.012 m/yr | 3 |
| Chlorophyll-a | ↑ Improving | -30.93 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Johnson Reservoir is a man-made reservoir impounded by the Johnson (completed 1910), built primarily for irrigation on the Fremont River; earth-type dam, 31 ft tall and 448 ft long.
- Normal storage
- 10,380 ac-ft
- Max storage
- 14,770 ac-ft
- Drainage area
- 36 sq mi
- Hazard class
- High
- Owner
- FREMONT IRRIGATION COMPANY
Source: USACE National Inventory of Dams, NID ID UT00153 · Operator website
EPA Impairment Status
Johnson Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit UT-L-14070003-010_00 · Official waterbody report · Matched by proximity (1.05 km)
County Ranking
Ranked #5 of 7 lakes in Sevier County
Nearby Lakes in Sevier County
Frequently asked questions about Johnson Reservoir
Where is Johnson Reservoir?
- Johnson Reservoir is a lake in Sevier County, Utah. LakeQuality grades it D for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Johnson Reservoir?
- Johnson Reservoir in Sevier County, Utah has a water quality grade of D (Nutrient-rich). Water clarity: 2 ft visibility. Phosphorus: 82 µg/L. Chlorophyll-a (algae): 29.1 µg/L.
Is Johnson Reservoir safe to swim in?
- The D is nutrients and algae, not a swimming clearance. Johnson Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
How deep is Johnson Reservoir?
- No published bathymetric survey covers Johnson Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 17 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Are there boat ramps on Johnson Reservoir?
- Johnson Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Johnson Reservoir. Public access is listed as yes.
Are there campgrounds on Johnson Reservoir?
- Johnson Reservoir has 3 public campgrounds from USGS The National Map within 5 km, including Paiute Campground, Tasha Equestrian Campground, Frying Pan Campground. This is a location join, not a booking. Cabins and hotels are listed separately; campsite reservations use the official link when the source provides one.
Explore Johnson Reservoir across LakeQuality
More Utah Lake Rankings
Other Grade D Lakes in Utah
Eutrophic Lakes in Utah
Where this data comes from
24 measurements from 1 monitoring station, 2013–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX24 samples · 2013–2025
Analytical methods
- Field Measurements
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
Grade thresholds from the EPA National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See how grades are calculated and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Lake size & watershed from HydroLAKES (HydroSHEDS)
Named boat-access points from the USGS National Boat Ramps inventory
Public campgrounds from USGS The National Map Structures, within about 3 miles