Willow Creek Reservoir
Yavapai County, Arizona460 acresView mapDirections
Not enough samples to grade — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years). No letter yet. Here is what we do have.
- Impaired · Nutrients (phosphorus, nitrogen)
- Limited data
Willow Creek Reservoir in Yavapai County, Arizona is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 460 acres.
- Area
- 460 acres
- Trend
- ↑ Improving
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Watch Willow Creek Reservoir’s letter
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Why Willow Creek Reservoir has no grade
We grade a lake only when the monitoring record supports a letter: at least three phosphorus or chlorophyll-a samples in the last ten years, scored against EPA National Lakes Assessment thresholds for this lake’s ecoregion. For Willow Creek Reservoir, no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years).
Not Rated is not an F. It is EPA Integrated Reporting Category 3 — insufficient information. The water here may be excellent or poor; nobody has measured enough of it to say. Everything below that has been measured is still reported on this page.
Sampling is run by ADEQ and volunteer programs, and published through the EPA Water Quality Portal. Read the full grading methodology.
Willow Creek Reservoir is a 460-acre lake in Yavapai County, Arizona. Overall water quality is improving over recent sampling years.
Source: EPA Water Quality Portal sampling records, ADEQ, last sampled 2022-04-12. Grade methodology: LakeQuality methodology.
Swimming Safety
Not ratedLimited data
The letter is not a swimming clearance. Willow Creek Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity. Check local advisories before you swim.
Water quality measurements for Willow Creek Reservoir
These readings exist but are not enough for an A–F grade — see why.
No clarity data.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | No recent samples | |
| Chlorophyll-a (Algae) | No recent samples |
Lake Details
| Characteristic | Value |
|---|---|
| Surface Area | 460 acres |
No bathymetric survey has been published for Willow Creek Reservoir, so its depth is not documented here.
Fishing Willow Creek Reservoir
Water Quality Trend: ↑ Improving
Based on 7 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Water Clarity | ↓ Declining | -0.206 m/yr | 3 |
| Phosphorus | ↑ Improving | -13.75 µg/L/yr | 7 |
| Chlorophyll-a | ↑ Improving | -8.26 µg/L/yr | 2 |
Reservoir Info (USACE NID)
Willow Creek Reservoir is a man-made reservoir impounded by the Willow Creek (completed 1936), built primarily for irrigation on the Willow Creek; arch-type dam, 99 ft tall and 297 ft long.
- Surface area
- 460 ac
- Normal storage
- 5,980 ac-ft
- Max storage
- 7,800 ac-ft
- Drainage area
- 25 sq mi
- Hazard class
- High
- Owner
- CITY OF PRESCOTT
All listed purposes: Irrigation;Recreation;Water Supply.
Source: USACE National Inventory of Dams, NID ID AZ00019 · Operator website
EPA Impairment Status
Willow Creek Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2024 EPA reporting cycle (IR category 4A).
Causes of impairment
A Total Maximum Daily Load (TMDL) plan has been approved.
Source: EPA ATTAINS assessment unit AZL15060202-1590_00 · Official waterbody report · Matched by proximity (2 km)
Graded lakes near Willow Creek Reservoir
Willow Creek Reservoir has no grade, but these lakes within a short drive do.
Nearby Lakes in Yavapai County
Frequently asked questions about Willow Creek Reservoir
Where is Willow Creek Reservoir?
- Willow Creek Reservoir is a lake in Yavapai County, Arizona. LakeQuality has not rated this lake (UNRATED) — no nutrient or algae measurement meets the evidence bar (at least 3 samples within 10 years).
What is the water quality grade for Willow Creek Reservoir?
- Willow Creek Reservoir in Yavapai County, Arizona is not rated for water quality — its monitoring record does not meet the evidence bar. Surface area: 460 acres.
Is Willow Creek Reservoir safe to swim in?
- The letter is not a swimming clearance. Willow Creek Reservoir is listed impaired under Clean Water Act §303(d) (IR 4A) for nutrients (phosphorus, nitrogen), oxygen depletion (low DO), pH / acidity. Check local advisories before you swim.
Explore Willow Creek Reservoir across LakeQuality
Planning a trip around Montezuma Castle?
Willow Creek Reservoir is about 35 miles from Montezuma Castle National Monument. 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 Montezuma Castle →More Arizona Lake Rankings
Other Lakes in Arizona
Where this data comes from
6 measurements from 1 monitoring station, 2021–2022. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Great Lakes Environmental Center
GLEC6 samples · 2021–2022
Analytical methods
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
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