Forsyth Reservoir
Sevier County, UtahView mapDirections
Utah DWQ publishes the water-quality measurements for Forsyth Reservoir. Here is what has been measured.
- Impaired · Nutrients (phosphorus, nitrogen)
- 19 ft max depth
- Limited data
Forsyth Reservoir in Sevier County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 13.8 ft visibility. Chlorophyll-a (algae): 4.7 µg/L.
Forsyth Reservoir is a lake in Sevier County, Utah with an estimated average depth of about 19 feet. Overall water quality is declining over recent sampling years.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2019-08-27. Methodology: how these readings are compared.
What Forsyth Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water13.8 ft of visibility
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Forsyth Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Forsyth 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 Forsyth Reservoir
These are the measurements Utah DWQ publishes for Forsyth Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Good clarity, visible to about 13.8 ft. Chlorophyll-a 4.7 µg/L. TSI 43.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 13.8ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | No reading The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. | |
| Chlorophyll-a (algae) | 4.7µg/L | Measured, not scored The green pigment in algae — a direct measure of how much algae is in the water. |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 43 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Forsyth Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Max depth
~19 ft est.
Depth marked “est.” is a modeled maximum from GLOBathy (Khazaei et al. 2022, CC0), not a measured survey. Utah has not published bathymetry for Forsyth Reservoir.
Lake Size & Watershed
Watershed (drainage) area
77 sq mi
HydroLAKES / HydroSHEDS
Surface area
136 acres
HydroLAKES / HydroSHEDS
Shoreline
3.1 mi
HydroLAKES / HydroSHEDS
Elevation
7,999 ft
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.
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Fishing Forsyth Reservoir
Water quality readings over time
2 seasons of samples on record (2013–2019). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Worsening2 years
Reservoir Info (USACE NID)
Forsyth Reservoir is a man-made reservoir impounded by the Forsyth (completed 1922), built primarily for irrigation on the U M Creek; earth-type dam, 65 ft tall and 355 ft long.
- Normal storage
- 3,639 ac-ft
- Max storage
- 5,670 ac-ft
- Drainage area
- 73.9 sq mi
- Hazard class
- High
- Owner
- FREMONT IRRIGATION COMPANY
Source: USACE National Inventory of Dams, NID ID UT00117 · Operator website
EPA Impairment Status
Forsyth Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
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-14070003-019_00 · Official waterbody report
Nearby Lakes in Sevier County
Frequently asked questions about Forsyth Reservoir
Where is Forsyth Reservoir?
- Forsyth 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 Forsyth Reservoir?
- Forsyth Reservoir in Sevier County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 13.8 ft visibility. Chlorophyll-a (algae): 4.7 µg/L.
Is Forsyth Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Forsyth 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 Forsyth Reservoir?
- No published bathymetric survey covers Forsyth Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 19 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
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Where this data comes from
22 measurements from 1 monitoring station, 2013–2019. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX22 samples · 2013–2019
Analytical methods
- Field Measurements
- 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
Lake size & watershed from HydroLAKES (HydroSHEDS)