Kolob Reservoir
Washington County, UtahView mapDirections
Utah DWQ publishes the water-quality measurements for Kolob Reservoir. Here is what has been measured.
- Mesotrophic
- Limited data
Kolob Reservoir in Washington County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 10.5 ft visibility. Phosphorus: 14.3 µg/L. Chlorophyll-a (algae): 2.1 µg/L.
Kolob Reservoir is a mesotrophic lake in Washington County, Utah. Overall water quality is improving over recent sampling years. Compared to the 9 other monitored lakes in Washington County, Kolob Reservoir ranks #8 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2025-08-18. Methodology: how these readings are compared.
What Kolob Reservoir is good for
From access and monitoring records, not editorial picks.
- Clear water10.5 ft of visibility
Swimming conditions
Readings onlyLimited data
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 Kolob 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 Kolob Reservoir
These are the measurements Utah DWQ publishes for Kolob 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 10.5 ft. Phosphorus 14.3 µg/L. Chlorophyll-a 2.1 µg/L. TSI 41.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 10.5ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 14.3µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2.1µg/L | Fair 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 Kolob Reservoir
Answers come straight from the public measurements and survey records on this page.
Stays via Stay22
Stays near Kolob Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Kolob Reservoir in Washington County, Utah — live availability and prices for your trip. Switch the map to Satellite to see the lake and how close each stay is to the water.
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Fishing Kolob Reservoir
Water quality readings over time
2 seasons of samples on record (2019–2025). Calling a direction takes at least 4 years of the same measurement.
Water clarity
Improving2 years
Chlorophyll-a
Improving-0.5 µg/L/yr2 years
Reservoir Info (USACE NID)
Kolob Reservoir is a man-made reservoir impounded by the Kolob Creek (completed 1956), built primarily for irrigation on the Kolob Creek; earth-type dam, 61 ft tall and 686 ft long.
- Normal storage
- 5,586 ac-ft
- Max storage
- 7,189 ac-ft
- Drainage area
- 8 sq mi
- Hazard class
- High
- Owner
- WASHINGTON COUNTY WATER CONSERVANCY DIST
Source: USACE National Inventory of Dams, NID ID UT00164 · Operator website · Matched by proximity (0.18 km)
Nearby Lakes in Washington County
Frequently asked questions about Kolob Reservoir
Where is Kolob Reservoir?
- Kolob Reservoir is a lake in Washington County, Utah. Its water-quality measurements are published by Utah DWQ and shown on this page as reported.
What is the water quality of Kolob Reservoir?
- Kolob Reservoir in Washington County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 10.5 ft visibility. Phosphorus: 14.3 µg/L. Chlorophyll-a (algae): 2.1 µg/L.
Is Kolob Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Kolob Reservoir across LakeQuality
Planning a trip around Zion?
Kolob Reservoir is about 9 miles from Zion National Park. Crowds there swing hard by season, so the month you pick changes both how busy the park is and what lodging costs.
Best time to visit Zion →More lakes in Utah
Other Lakes in Utah
Mesotrophic Lakes in Utah
Where this data comes from
18 measurements from 1 monitoring station, 2019–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX18 samples · 2019–2025
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.