Boulder Reservoir
Washoe County, NevadaView mapDirections
NDEP publishes the water-quality measurements for Boulder Reservoir. Here is what has been measured.
- Eutrophic
- Impaired · Metals (other than mercury)
- Limited data
Boulder Reservoir in Washoe County, Nevada has water-quality measurements published by NDEP, shown here as reported. Phosphorus: 50 µg/L.
Boulder Reservoir is a productive, nutrient-rich eutrophic lake in Washoe County, Nevada. 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. Methodology: how these readings are compared.
Swimming conditions
Readings onlyRecreation use not supported
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. 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.
Whether Boulder Reservoir is safe to swim in today is a call for the Nevada Division of Environmental Protection and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Boulder Reservoir
These are the measurements NDEP publishes for Boulder Reservoir, shown as reported. The condition class beside each reading is the EPA National Lakes Assessment class for this lake’s ecoregion.
No clarity data. Phosphorus 50 µg/L. TSI 61.
| Measure | Reading | Where it sits |
|---|---|---|
| Water clarity (Secchi depth) | No reading How deep a black-and-white disk stays visible from the surface. Higher is clearer. | |
| Total phosphorus | 50µg/L | Fair GoodFairPoor |
| Chlorophyll-a (algae) | No reading The green pigment in algae — a direct measure of how much algae is in the water. | |
| Trophic state (TSI)Carlson's 0–100 index of how much algae a lake can support, from clarity, phosphorus and chlorophyll-a. | 61 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
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Fishing Boulder Reservoir
Water Quality Trend: Worsening
Based on 4 years of monitoring (2016–2019).
Phosphorus
Worsening+3 µg/L/yr4 years
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
Designated uses not supporting: Drinking water, Aquatic life, Recreation.
Source: EPA ATTAINS assessment unit NV01-NW-01-A_00 · Official waterbody report
Nearby Lakes in Washoe County
Frequently asked questions about Boulder Reservoir
Where is Boulder Reservoir?
- Boulder Reservoir is a lake in Washoe County, Nevada. Its water-quality measurements are published by NDEP and shown on this page as reported.
What is the water quality of Boulder Reservoir?
- Boulder Reservoir in Washoe County, Nevada has water-quality measurements published by NDEP, shown here as reported. Phosphorus: 50 µg/L.
Is Boulder Reservoir safe to swim in?
- Nutrient and algae readings are 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.
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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)
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