Boulder Reservoir
Washoe County, NevadaView mapDirections
Nutrients and algae sit mid-range for this region.
↓ down from B at the last regrade
- Eutrophic
- Impaired · Metals (other than mercury)
- #2 of 10 in the county
- Limited data
Boulder Reservoir in Washoe County, Nevada has a water quality grade of C (Fair). Phosphorus: 50 µg/L.
- Type
- Eutrophic
- Phosphorus
- 50 µg/L
- Trend
- ↓ Declining
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Watch Boulder Reservoir’s letter
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Boulder Reservoir is a productive, nutrient-rich eutrophic lake in Washoe County, Nevada. Water quality is graded C based on 1 sampling years through 2019. Overall water quality is declining over recent sampling years. Compared to the 9 other monitored lakes in Washoe County, Boulder Reservoir ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, NDEP, last sampled 2019-07-23. Grade methodology: LakeQuality methodology.
Swimming Safety
Grade onlyLimited data
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. Boulder Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury), nutrients (phosphorus, nitrogen), pH / acidity. Check local advisories before you swim.
Water Quality Grade: C (Fair)
No clarity data. Phosphorus 50 µg/L. TSI 61. The letter is not a swimming clearance.
| Metric | Value | Grade |
|---|---|---|
| Water Clarity (Secchi Depth) | No recent samples | |
| Phosphorus | 50 µg/L | Fair |
| Chlorophyll-a (Algae) | No recent samples | |
| Trophic State Index (TSI) | 61 | Eutrophic |
High nutrients, frequent algae, reduced clarity
Fishing Boulder Reservoir
Water Quality Trend: ↓ Declining
Based on 4 years of monitoring data (2020-2025).
| Metric | Trend | Change/Year | Years |
|---|---|---|---|
| Phosphorus | ↓ Declining | +3 µg/L/yr | 4 |
EPA Impairment Status
Boulder Reservoir is officially listed as impaired under Clean Water Act §303(d) in the 2022 EPA reporting cycle (IR category 5).
Causes of impairment
Source: EPA ATTAINS assessment unit NV01-NW-01-A_00 · Official waterbody report
County Ranking
Ranked #2 of 10 lakes in Washoe County
Nearby Lakes in Washoe County
Frequently asked questions about Boulder Reservoir
Where is Boulder Reservoir?
- Boulder Reservoir is a lake in Washoe County, Nevada. LakeQuality grades it C for nutrients and algae. The letter is not a swimming clearance.
What is the water quality grade for Boulder Reservoir?
- Boulder Reservoir in Washoe County, Nevada has a water quality grade of C (Fair). Phosphorus: 50 µg/L.
Is Boulder Reservoir safe to swim in?
- The C is nutrients and algae, not a swimming clearance. Boulder Reservoir is listed impaired under Clean Water Act §303(d) (IR 5) for metals (other than mercury), nutrients (phosphorus, nitrogen), pH / acidity. Check local advisories before you swim.
Explore Boulder Reservoir across LakeQuality
4 thermal springs within 19.3 mi, nearest Twin (Vya) Spring
Species activity outlook by water temperature and season
Where to stay at Nevada's top lakes, each with its grade
High nutrients, frequent algae, reduced clarity
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Other Grade C Lakes in Nevada
Eutrophic Lakes in Nevada
Where this data comes from
7 measurements from 1 monitoring station, 2016–2019. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Nevada Division of Environmental Protection
21NEV1_WQX7 samples · 2016–2019
Analytical methods
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 4500 P E ~ Phosphorus by Ascorbic Acid
- 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.
Other records on this page
Impairment status from EPA ATTAINS 303(d) database