Onion Valley Reservoir @ Dam
Humboldt County, Nevada101 acresView mapDirections
This is the name NDEP records for this water. It can describe one sampling location rather than the water as a whole.
NDEP publishes the water-quality measurements for Onion Valley Reservoir @ Dam. Here is what has been measured.
- Eutrophic
Onion Valley Reservoir @ Dam in Humboldt County, Nevada has water-quality measurements published by NDEP, shown here as reported. Phosphorus: 50 µg/L. Chlorophyll-a (algae): 4.6 µg/L. Surface area: 101 acres.
Onion Valley Reservoir @ Dam is a 101-acre productive, nutrient-rich eutrophic lake in Humboldt County, Nevada. Overall water quality is declining over recent sampling years. Compared to the 3 other monitored lakes in Humboldt County, Onion Valley Reservoir @ Dam ranks #2 for water quality.
Source: EPA Water Quality Portal sampling records, NDEP, last sampled 2021-10-05. Methodology: how these readings are compared.
Onion Valley Reservoir @ Dam covers about 100 acres in Humboldt County. If you are planning to stay, you can search lake houses and cabins around Onion Valley Reservoir @ Dam on Vrbo, or look for a hotel room near the lake on Booking.com or Expedia.
Swimming conditions
Readings onlyModerate algae
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. Check local advisories before you swim.
Whether Onion Valley Reservoir @ Dam 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 Onion Valley Reservoir @ Dam
These are the measurements NDEP publishes for Onion Valley Reservoir @ Dam, 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. Chlorophyll-a 4.6 µg/L. TSI 53.
| 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) | 4.6µg/L | Measured, not scored 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. | 53 | Eutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
High nutrients, frequent algae, reduced clarity
Ask about Onion Valley Reservoir @ Dam
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
101 acres
No bathymetric survey has been published for Onion Valley Reservoir @ Dam, so its depth is not documented here.
Stays via Stay22
Stays near Onion Valley Reservoir @ Dam
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Fishing Onion Valley Reservoir @ Dam
Water Quality Trend: Worsening
Based on 7 years of monitoring (2012–2021).
Phosphorus
Worsening+21.56 µg/L/yr7 years
Chlorophyll-a
Worsening+0.46 µg/L/yr3 years
Reservoir Info (USACE NID)
Onion Valley Reservoir @ Dam is a man-made reservoir impounded by the Onion Dam, built primarily for irrigation on the East Fork Alder Creek; earth-type dam, 54 ft tall and 320 ft long.
- Surface area
- 101 ac
- Normal storage
- 1,500 ac-ft
- Max storage
- 1,500 ac-ft
- Drainage area
- 3.1 sq mi
- Hazard class
- Significant
- Owner
- ALDER CREEK RANCH LLC
All listed purposes: Irrigation;Recreation.
Source: USACE National Inventory of Dams, NID ID NV00005 · Operator website · Matched by proximity (0.16 km)
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Frequently asked questions about Onion Valley Reservoir @ Dam
Where is Onion Valley Reservoir @ Dam?
- Onion Valley Reservoir @ Dam is in Humboldt County, Nevada. This is the name NDEP records for this water. It can describe one sampling location rather than the water as a whole. Its water-quality measurements are published by NDEP and shown on this page as reported.
What is the water quality of Onion Valley Reservoir @ Dam?
- Onion Valley Reservoir @ Dam in Humboldt County, Nevada has water-quality measurements published by NDEP, shown here as reported. Phosphorus: 50 µg/L. Chlorophyll-a (algae): 4.6 µg/L. Surface area: 101 acres.
Is Onion Valley Reservoir @ Dam safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Explore Onion Valley Reservoir @ Dam across LakeQuality
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Where this data comes from
21 measurements from 1 monitoring station, 2016–2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Nevada Division of Environmental Protection
21NEV1_WQX21 samples · 2016–2021
Analytical methods
- 4500 P E ~ Phosphorus in Water by Colorimetry- Ascorbic Acid Method
- 4500 P E ~ Phosphorus by Ascorbic Acid
- Phosphorus by Two Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- 2130 B ~ Nephelometric Method
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.