Nine Mile Reservoir
Sanpete 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 · Nutrients (phosphorus, nitrogen)
- #5 of 11 in the county
- 23 ft max depth
- Limited data
Nine Mile Reservoir in Sanpete County, Utah has a water quality grade of A (Excellent). Water clarity: 9.3 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 2.5 µg/L.
- Clarity
- 9.3 ft
- Max depth
- ~23 ft est.
- Type
- Mesotrophic
- Phosphorus
- 13 µg/L
- Chlorophyll-a
- 2.5 µg/L
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Watch Nine Mile Reservoir’s letter
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Nine Mile Reservoir is a mesotrophic lake in Sanpete County, Utah with an estimated average depth of about 23 feet. Water quality is graded A based on 2 sampling years through 2020. Compared to the 10 other monitored lakes in Sanpete County, Nine Mile Reservoir ranks #5 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2020-08-03. 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. Nine Mile 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.
Water Quality Grade: A (Excellent)
Moderate clarity, visible to about 9.3 ft. Phosphorus 13 µg/L. Chlorophyll-a 2.5 µg/L. TSI 42. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 9.3 ft | Not graded |
| Phosphorus | 13 µg/L | Good |
| Chlorophyll-a (Algae) | 2.5 µg/L | Good |
| Trophic State Index (TSI) | 42 | Mesotrophic |
Moderate nutrients, good water quality
Lake Details
| Characteristic | Value |
|---|---|
| Maximum Depth | ~23 ft est. |
| Average Depth | ~16 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 Nine Mile 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 Nine Mile Reservoir
Reservoir Info (USACE NID)
Nine Mile Reservoir is a man-made reservoir impounded by the Ninemile (completed 1900), built primarily for irrigation on the Nine Mile Creek; earth-type dam, 55 ft tall and 825 ft long.
- Normal storage
- 3,500 ac-ft
- Max storage
- 4,300 ac-ft
- Drainage area
- 4 sq mi
- Hazard class
- High
- Owner
- GUNNISON IRRIGATION COMPANY
Source: USACE National Inventory of Dams, NID ID UT00138 · Operator website
EPA Impairment Status
Nine Mile 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-16030004-001_00 · Official waterbody report
County Ranking
Ranked #5 of 11 lakes in Sanpete County
Nearby Lakes in Sanpete County
Frequently asked questions about Nine Mile Reservoir
Where is Nine Mile Reservoir?
- Nine Mile Reservoir is a lake in Sanpete County, Utah. LakeQuality grades it A for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Nine Mile Reservoir?
- Nine Mile Reservoir in Sanpete County, Utah has a water quality grade of A (Excellent). Water clarity: 9.3 ft visibility. Phosphorus: 13 µg/L. Chlorophyll-a (algae): 2.5 µg/L.
Is Nine Mile Reservoir safe to swim in?
- The A is nutrients and algae, not a swimming clearance. Nine Mile 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.
How deep is Nine Mile Reservoir?
- No published bathymetric survey covers Nine Mile Reservoir, so its depth has not been measured. The HydroLAKES global model estimates an average depth of about 23 feet, but that is a modelled estimate derived from surrounding terrain rather than a measurement on the water, so treat it as approximate.
Explore Nine Mile Reservoir across LakeQuality
3 thermal springs within 14.5 mi, nearest Sterling (Peacock) Warm Spring
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Where this data comes from
11 measurements from 1 monitoring station, 2020. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX11 samples · 2020
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)