Koosharem Reservoir
Sevier County, UtahView mapDirections
Utah DWQ publishes the water-quality measurements for Koosharem Reservoir. Here is what has been measured.
- Hypereutrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- Limited data
Koosharem Reservoir in Sevier County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 7.2 ft visibility. Phosphorus: 194 µg/L. Chlorophyll-a (algae): 58.4 µg/L.
Koosharem Reservoir is a highly nutrient-loaded hypereutrophic lake in Sevier County, Utah. Overall water quality is declining over recent sampling years. Public access is available with 1 public boat landing. Compared to the 6 other monitored lakes in Sevier County, Koosharem Reservoir ranks #7 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2020-08-26. Methodology: how these readings are compared.
What Koosharem Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
Swimming conditions
Readings onlyLimited data
Based on clarity and algae readings from past sampling — there is no live water temperature and a current cyanobacteria reading for this lake. Check your state or county health department before you swim.
Nutrient and algae readings are not a swimming clearance. Koosharem Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity, temperature. Check local advisories before you swim.
Whether Koosharem Reservoir is safe to swim in today is a call for the Utah Division of Water Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Koosharem Reservoir
These are the measurements Utah DWQ publishes for Koosharem Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Moderate clarity, visible to about 7.2 ft. Phosphorus 194 µg/L. Chlorophyll-a 58.4 µg/L. TSI 66.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 7.2ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 194µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 58.4µg/L | Poor GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 66 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Koosharem Reservoir
Answers come straight from the public measurements and survey records on this page.
Recreation & Access
- Koosharem Reservoir Recreation SiteSemi-private
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Koosharem Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Koosharem 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 readings cover nutrients and algae, not lodging. Cabins and rentals around Koosharem Reservoir are listed below.
Top-rated places to stay near Koosharem Reservoir
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Fishing Koosharem Reservoir
Water quality readings over time
3 seasons of samples on record (2014–2020). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Stable3 years
Chlorophyll-a
Worsening+6.4 µg/L/yr2 years
Reservoir Info (USACE NID)
Koosharem Reservoir is a man-made reservoir impounded by the Koosharem (completed 1919), built primarily for irrigation on the Otter Creek; earth-type dam, 30 ft tall and 1,950 ft long.
- Normal storage
- 3,044.6 ac-ft
- Max storage
- 7,369.8 ac-ft
- Drainage area
- 63 sq mi
- Hazard class
- High
- Owner
- KOOSHAREM IRRIGATION COMPANY
Source: USACE National Inventory of Dams, NID ID UT00165 · Operator website
EPA Impairment Status
Koosharem Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Designated uses not supporting: Aquatic life.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit UT-L-16030002-011_00 · Official waterbody report
Nearby Lakes in Sevier County
Frequently asked questions about Koosharem Reservoir
Where is Koosharem Reservoir?
- Koosharem Reservoir is a lake in Sevier County, Utah. Its water-quality measurements are published by Utah DWQ and shown on this page as reported.
What is the water quality of Koosharem Reservoir?
- Koosharem Reservoir in Sevier County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 7.2 ft visibility. Phosphorus: 194 µg/L. Chlorophyll-a (algae): 58.4 µg/L.
Is Koosharem Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Koosharem Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity, temperature. Check local advisories before you swim.
Are there boat ramps on Koosharem Reservoir?
- Koosharem Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Koosharem Reservoir Recreation Site.
Can I fish at Koosharem Reservoir?
- Koosharem Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Utah's fish and wildlife agency, so check its current regulations before you go.
Explore Koosharem Reservoir across LakeQuality
4 thermal springs within 18.4 mi, nearest Red Hill Hot Spring
Species activity outlook by water temperature and season
Where to stay at Utah's top lakes, each with its readings
Utah's cleanest lakes, ranked on agency measurements
Planning a trip around Capitol Reef?
Koosharem Reservoir is about 39 miles from Capitol Reef 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 Capitol Reef →More lakes in Utah
Other Lakes in Utah
Hypereutrophic Lakes in Utah
Where this data comes from
22 measurements from 1 monitoring station, 2014–2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX22 samples · 2014–2020
Analytical methods
- Field Measurements
- Phosphorus by Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
Monitoring station identifiers (1)
EPA condition classes from the National Lakes Assessment (EPA 841-R-24-006, Table 6-3), applied by ecoregion. See where the data comes from and data sources.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Named boat-access points from the USGS National Boat Ramps inventory