Gunlock Reservoir
Washington County, UtahView mapDirections
Utah DWQ publishes the water-quality measurements for Gunlock Reservoir. Here is what has been measured.
- Mesotrophic
- Impaired · Nutrients (phosphorus, nitrogen)
- Public access
- Limited data
Gunlock Reservoir in Washington County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 4.6 ft visibility. Phosphorus: 21 µg/L. Chlorophyll-a (algae): 2.9 µg/L.
Gunlock Reservoir is a mesotrophic lake in Washington County, Utah. Limited fish-species data available. Public access is available with 1 public boat landing. Compared to the 9 other monitored lakes in Washington County, Gunlock Reservoir ranks #1 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2025-08-19. Methodology: how these readings are compared.
Gunlock Reservoir has one public boat landing. Vrbo is where to look for cabins and lake homes around Gunlock Reservoir, and Booking.com and Expedia search hotels near the lake for your dates.
What Gunlock Reservoir is good for
From access and monitoring records, not editorial picks.
- Boat launch1 documented ramp
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. Gunlock Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Whether Gunlock 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 Gunlock Reservoir
These are the measurements Utah DWQ publishes for Gunlock Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
Murky, only visible to about 4.6 ft. Phosphorus 21 µg/L. Chlorophyll-a 2.9 µg/L. TSI 48.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | 4.6ft | Measured, not scored How deep a black-and-white disk stays visible from the surface. Higher is clearer. |
| Total phosphorus | 21µg/L | Good GoodFairPoor |
| Chlorophyll-a (algae) | 2.9µg/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. | 48 | Mesotrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Moderate nutrients, good water quality
Ask about Gunlock Reservoir
Answers come straight from the public measurements and survey records on this page.
Recreation & Access
- Gunlock State ParkPublic
Named access points in the USGS National Boat Ramps inventory, within about 3 miles. More lakes with boat ramps
Stays via Stay22
Stays near Gunlock Reservoir
Compare lakeside cabins, hotels, and vacation rentals near Gunlock 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.
Top-rated places to stay near Gunlock Reservoir
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Fishing Gunlock Reservoir
Water Quality Trend: Stable
Based on 4 years of monitoring (2012–2025).
Water clarity
Stable4 years
Chlorophyll-a
Stable+0.05 µg/L/yr2 years
Reservoir Info (USACE NID)
Gunlock Reservoir is a man-made reservoir impounded by the Gunlock (completed 1970), built primarily for irrigation on the Santa Clara River; earth-type dam, 117 ft tall and 1,400 ft long.
- Normal storage
- 10,884 ac-ft
- Max storage
- 15,041 ac-ft
- Drainage area
- 306 sq mi
- Hazard class
- High
- Owner
- LOWER GUNLOCK RESERVOIR CORPORATION
Source: USACE National Inventory of Dams, NID ID UT00129 · Operator website
EPA Impairment Status
Gunlock Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
Designated uses not supporting: Aquatic life.
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit UT-L-15010008-001_00 · Official waterbody report
Nearby Lakes in Washington County
Frequently asked questions about Gunlock Reservoir
Where is Gunlock Reservoir?
- Gunlock 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 Gunlock Reservoir?
- Gunlock Reservoir in Washington County, Utah has water-quality measurements published by Utah DWQ, shown here as reported. Water clarity: 4.6 ft visibility. Phosphorus: 21 µg/L. Chlorophyll-a (algae): 2.9 µg/L.
Is Gunlock Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Gunlock Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen). Check local advisories before you swim.
Are there boat ramps on Gunlock Reservoir?
- Gunlock Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Named access points include Gunlock State Park. Public access is listed as yes.
Can I fish at Gunlock Reservoir?
- Gunlock Reservoir has 1 documented boat landing in the USGS National Boat Ramps inventory. Seasons, size and bag limits, and whether you need a license are set by Utah's fish and wildlife agency, so check its current regulations before you go.
Explore Gunlock Reservoir across LakeQuality
4 thermal springs within 15.8 mi, nearest Veyo Hot Spring
19.2 mi away · cable-pulled, no boat wake
Species activity outlook by water temperature and season
Where to stay at Utah's top lakes, each with its readings
Utah's cleanest lakes, ranked on agency measurements
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Where this data comes from
38 measurements from 1 monitoring station, 2013–2025. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX38 samples · 2013–2025
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.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database
Named boat-access points from the USGS National Boat Ramps inventory