Grantsville Reservoir
Tooele County, UtahView mapDirections
Clarity, phosphorus, and algae all sit in the cleanest band for this region.
↑ up from B at the last regrade
- Mesotrophic
- Impaired · Oxygen depletion (low DO)
- #2 of 4 in the county
- 24 ft max depth
- Limited data
Grantsville Reservoir in Tooele County, Utah has a water quality grade of A (Excellent). Water clarity: 5.9 ft visibility. Phosphorus: 19 µg/L. Chlorophyll-a (algae): 4 µg/L.
- Clarity
- 5.9 ft
- Max depth
- ~24 ft est.
- Type
- Mesotrophic
- Phosphorus
- 19 µg/L
- Chlorophyll-a
- 4 µg/L
- Trend
- → Stable
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Watch Grantsville Reservoir’s letter
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Grantsville Reservoir is a mesotrophic lake in Tooele County, Utah with an estimated average depth of about 24 feet. Water quality is graded A based on 2 sampling years through 2024. Water clarity is improving over recent sampling years. Compared to the 3 other monitored lakes in Tooele County, Grantsville Reservoir ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2024-09-03. Grade methodology: LakeQuality methodology.
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 A is nutrients and algae, not a swimming clearance. Grantsville Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for oxygen depletion (low DO), pH / acidity, temperature. Check local advisories before you swim.
Water Quality Grade: A (Excellent)
Murky, only visible to about 5.9 ft. Phosphorus 19 µg/L. Chlorophyll-a 4 µg/L. TSI 47. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 5.9 ft | Not graded |
| Phosphorus | 19 µg/L | Good |
| Chlorophyll-a (Algae) | 4 µg/L | Good |
| Trophic State Index (TSI) | 47 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~24 ft est. |
| Average Depth | ~13 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 Grantsville 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 Grantsville Reservoir
Water Quality Trend: → Stable
Based on 3 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↑ Improving | +0.046 m/yr | 3 |
| Chlorophyll-a | ↓ Declining | +0.11 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Grantsville Reservoir is a man-made reservoir impounded by the Grantsville (completed 1984), built primarily for irrigation on the So Willow, No Willow, Et Al; earth-type dam, 82 ft tall and 5,376 ft long.
- Normal storage
- 3,370 ac-ft
- Max storage
- 3,885 ac-ft
- Drainage area
- 3 sq mi
- Hazard class
- High
- Owner
- GRANTSVILLE IRRIGATION COMPANY
Source: USACE National Inventory of Dams, NID ID UT00343 · Operator website
EPA Impairment Status
Grantsville Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit UT-L-16020304-005_00 · Official waterbody report
County Ranking
Ranked #2 of 4 lakes in Tooele County
Nearby Lakes in Tooele County
Frequently asked questions about Grantsville Reservoir
Where is Grantsville Reservoir?
- Grantsville Reservoir is a lake in Tooele County, Utah. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Grantsville Reservoir?
- Grantsville Reservoir in Tooele County, Utah has a water quality grade of A (Excellent). Water clarity: 5.9 ft visibility. Phosphorus: 19 µg/L. Chlorophyll-a (algae): 4 µg/L.
Is Grantsville Reservoir safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Grantsville Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for oxygen depletion (low DO), pH / acidity, temperature. Check local advisories before you swim.
How deep is Grantsville Reservoir?
- No published bathymetric survey covers Grantsville Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 24 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Grantsville Reservoir across LakeQuality
4 thermal springs within 11.6 mi, nearest Grantsville Warm Springs
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Where this data comes from
19 measurements from 1 monitoring station, 2012–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX19 samples · 2012–2024
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)