Willard Bay Reservoir
Box Elder County, Utah9,950 acresView mapDirections
Nutrients and algae sit mid-range for this region.
- Eutrophic
- #7 of 15 in the county
Willard Bay Reservoir in Box Elder County, Utah has a water quality grade of C (Fair). Water clarity: 2.3 ft visibility. Phosphorus: 55 µg/L. Chlorophyll-a (algae): 7.9 µg/L. Surface area: 9950 acres.
- Clarity
- 2.3 ft
- Area
- 9,950 acres
- Type
- Eutrophic
- Phosphorus
- 55 µg/L
- Chlorophyll-a
- 7.9 µg/L
- Trend
- ↓ Declining
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Watch Willard Bay Reservoir’s letter
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Willard Bay Reservoir is a 9,950-acre productive, nutrient-rich eutrophic lake in Box Elder County, Utah. Water quality is graded C based on 2 sampling years through 2023. Overall water quality is declining over recent sampling years. Compared to the 14 other monitored lakes in Box Elder County, Willard Bay Reservoir ranks #7 for water quality.
Source: EPA Water Quality Portal sampling records, Utah DWQ, last sampled 2023-10-10. Grade methodology: LakeQuality methodology.
What Willard Bay Reservoir is good for
From access and monitoring records, not editorial picks.
- Big water9,950 acres
Swimming Safety
Grade onlyModerate
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 C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Water Quality Grade: C (Fair)
Very murky, less than 2.3 ft of visibility. Phosphorus 55 µg/L. Chlorophyll-a 7.9 µg/L. TSI 59. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | 2.3 ft | Not graded |
| Phosphorus | 55 µg/L | Fair |
| Chlorophyll-a (Algae) | 7.9 µg/L | Fair |
| Trophic State Index (TSI) | 59 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 9,950 acres |
No bathymetric survey has been published for Willard Bay Reservoir, so its depth is not documented here.
Fishing Willard Bay Reservoir
Water Quality Trend: ↓ Declining
Based on 6 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.133 m/yr | 6 |
| Phosphorus | ↓ Declining | +1.36 µg/L/yr | 4 |
| Chlorophyll-a | ↑ Improving | -2.07 µg/L/yr | 4 |
Reservoir Info (USACE NID)
Willard Bay Reservoir is a man-made reservoir impounded by the Arthur V. Watkins Dam (completed 1964), built primarily for irrigation on the Bear River Offstream; earth-type dam, 38 ft tall and 76,665 ft long.
- Surface area
- 9,950 ac
- Normal storage
- 215,500 ac-ft
- Max storage
- 223,000 ac-ft
- Drainage area
- 16 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
Source: USACE National Inventory of Dams, NID ID UT10112 · Operator website
County Ranking
Ranked #7 of 15 lakes in Box Elder County
Nearby Lakes in Box Elder County
Frequently asked questions about Willard Bay Reservoir
Where is Willard Bay Reservoir?
- Willard Bay Reservoir is a lake in Box Elder County, Utah. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Willard Bay Reservoir?
- Willard Bay Reservoir in Box Elder County, Utah has a water quality grade of C (Fair). Water clarity: 2.3 ft visibility. Phosphorus: 55 µg/L. Chlorophyll-a (algae): 7.9 µg/L. Surface area: 9950 acres.
Is Willard Bay Reservoir safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Check local advisories before you swim.
Explore Willard Bay Reservoir across LakeQuality
2 thermal springs within 18.1 mi, nearest Utah Hot Springs
Species activity outlook by water temperature and season
Where to stay at Utah's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
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Other Grade C Lakes in Utah
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Where this data comes from
72 measurements from 1 monitoring station, 2015–2023. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Utah Department Of Environmental Quality
UTAHDWQ_WQX72 samples · 2015–2023
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.