Moon Lake
Duchesne County, Utah773 acresView mapDirections
Utah DWQ publishes the water-quality measurements for Moon Lake. Here is what has been measured.
- Mesotrophic
Moon Lake in Duchesne County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 9.5 ft visibility. Phosphorus: 11.2 µg/L. Chlorophyll-a (algae): 2.7 µg/L. Surface area: 773 acres.
Moon Lake is a 773-acre mesotrophic lake in Duchesne County, Utah. Overall water quality is declining over recent sampling years. Compared to the 8 other monitored lakes in Duchesne County, Moon Lake ranks #3 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2024-08-21. Methodology: how these readings are compared.
Swimming conditions
Readings onlyLow algae
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. Check local advisories before you swim.
Whether Moon Lake 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 Moon Lake
These are the measurements Utah DWQ publishes for Moon Lake, 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 9.5 ft. Phosphorus 11.2 µg/L. Chlorophyll-a 2.7 µg/L. TSI 41.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 9.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 11.2µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2.7µg/L | Good GoodFairPoor |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 41 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Moon Lake
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
773 acres
No bathymetric survey has been published for Moon Lake, so its depth is not documented here.
Stays via Stay22
Stays near Moon Lake
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Fishing Moon Lake
Water quality readings over time
3 seasons of samples on record (2017–2024). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Worsening3 years
Phosphorus
Improving-0.6 µg/L/yr2 years
Chlorophyll-a
Worsening+1.6 µg/L/yr2 years
Reservoir Info (USACE NID)
Moon Lake is a man-made reservoir impounded by the Moon Lake Dam (completed 1938), built primarily for irrigation on the Lake Fork River; earth-type dam, 101 ft tall and 1,108 ft long.
- Surface area
- 773 ac
- Normal storage
- 49,500 ac-ft
- Max storage
- 49,500 ac-ft
- Drainage area
- 112.25 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
Source: USACE National Inventory of Dams, NID ID UT10128 · Operator website
Nearby Lakes in Duchesne County
Frequently asked questions about Moon Lake
Where is Moon Lake?
- Moon Lake is a lake in Duchesne County, Utah. Its water-quality measurements are published by Utah DWQ and shown on this page as reported.
What is the water quality of Moon Lake?
- Moon Lake in Duchesne County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 9.5 ft visibility. Phosphorus: 11.2 µg/L. Chlorophyll-a (algae): 2.7 µg/L. Surface area: 773 acres.
Is Moon Lake safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Moon Lake across LakeQuality
More lakes in Utah
Other Lakes in Utah
Mesotrophic Lakes in Utah
Where this data comes from
39 measurements from 1 monitoring station, 2017–2024. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX39 samples · 2017–2024
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.