Forsyth Reservoir
Sevier County, UtahView mapDirections
Not enough samples to grade — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. No letter yet. Here is what we do have.
- Impaired · Nutrients (phosphorus, nitrogen)
- 19 ft max depth
- Limited data
Forsyth Reservoir in Sevier County, Utah is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13.8 ft visibility. Chlorophyll-a (algae): 4.7 µg/L.
- Clarity
- 13.8 ft
- Max depth
- ~19 ft est.
- Chlorophyll-a
- 4.7 µg/L
- Trend
- ↓ Declining
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Watch Forsyth Reservoir’s letter
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Why Forsyth Reservoir has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Forsyth Reservoir, the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity. Sampling here has recorded water clarity and algae (chlorophyll-a), but not phosphorus.
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by Utah DWQ and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
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. Grade methodology: LakeQuality methodology.
What Forsyth Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water13.8 ft of visibility
Swimming Safety
Not ratedLimited data
The letter is 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.
Water quality measurements for Forsyth Reservoir
These readings exist but are not enough for an A–F grade — see why.
Good clarity, visible to about 13.8 ft. Chlorophyll-a 4.7 µg/L. TSI 43.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 13.8 ft | Not graded |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | 4.7 µg/L | Not graded |
| Trophic State Index (TSI) | 43 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum 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
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.
Fishing Forsyth Reservoir
Water Quality Trend: ↓ Declining
Based on 2 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.35 m/yr | 2 |
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
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit UT-L-14070003-019_00 · Official waterbody report
Graded lakes near Forsyth Reservoir
Forsyth Reservoir has no grade, but these lakes within a short drive do.
Nearby Lakes in Sevier County
Frequently asked questions about Forsyth Reservoir
Where is Forsyth Reservoir?
- Forsyth Reservoir is a lake in Sevier County, Utah. LakeQuality has not rated this lake (UNRATED) — the only measurement available is water clarity, which is not a water-quality indicator on its own — EPA's National Lakes Assessment does not grade clarity.
What is the water quality grade for Forsyth Reservoir?
- Forsyth Reservoir in Sevier County, Utah is not rated for water quality — its monitoring record does not meet the evidence bar. Water clarity: 13.8 ft visibility. Chlorophyll-a (algae): 4.7 µg/L.
Is Forsyth Reservoir safe to swim in?
- The letter is 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)
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)