Mann Creek Reservoir
Washington County, Idaho283 acresView mapDirections
Idaho DEQ publishes the water-quality measurements for Mann Creek Reservoir. Here is what has been measured.
- Limited data
Mann Creek Reservoir in Washington County, Idaho has water-quality measurements published by Idaho DEQ, shown here as reported. Phosphorus: 49 µg/L. Chlorophyll-a (algae): 179 µg/L. Surface area: 283 acres.
Mann Creek Reservoir is a 283-acre lake in Washington County, Idaho.
Source: EPA Water Quality Portal sampling records, IDEQ, last sampled 2021-07-21. Methodology: how these readings are compared.
Swimming conditions
No readingLimited data
Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
Whether Mann Creek Reservoir is safe to swim in today is a call for the Idaho Department of Environmental Quality and the county health department, who post current advisories. LakeQuality does not issue swimming clearances.
Water quality measurements for Mann Creek Reservoir
These are the measurements Idaho DEQ publishes for Mann Creek 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 49 µg/L. Chlorophyll-a 179 µg/L. TSI 71.
| 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 | 49µg/L | Measured, not scored The nutrient that most limits algae growth in freshwater. More phosphorus, more algae potential. |
| Chlorophyll-a (algae) | 179µg/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. | 71 | Hypereutrophic OligotrophicMesotrophicEutrophicHypereutrophic |
Very high nutrients, dense algae, poor clarity
Ask about Mann Creek Reservoir
Answers come straight from the public measurements and survey records on this page.
Lake Details
Surface area
283 acres
No bathymetric survey has been published for Mann Creek Reservoir, so its depth is not documented here.
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Reservoir Info (USACE NID)
Mann Creek Reservoir is a man-made reservoir impounded by the Mann Creek Dam (completed 1967), built primarily for irrigation on the Mann Creek; earth-type dam, 148 ft tall and 1,176 ft long.
- Surface area
- 283 ac
- Max storage
- 12,536 ac-ft
- Drainage area
- 55.98 sq mi
- Hazard class
- High
- Owner
- BUREAU OF RECLAMATION
Source: USACE National Inventory of Dams, NID ID ID00285 · Operator website
Nearby Lakes in Washington County
Frequently asked questions about Mann Creek Reservoir
Where is Mann Creek Reservoir?
- Mann Creek Reservoir is a lake in Washington County, Idaho. Its water-quality measurements are published by Idaho DEQ and shown on this page as reported.
What is the water quality of Mann Creek Reservoir?
- Mann Creek Reservoir in Washington County, Idaho has water-quality measurements published by Idaho DEQ, shown here as reported. Phosphorus: 49 µg/L. Chlorophyll-a (algae): 179 µg/L. Surface area: 283 acres.
Is Mann Creek Reservoir safe to swim in?
- Nutrient and algae readings are not a swimming clearance. Check local advisories before you swim.
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Where this data comes from
3 measurements from 1 monitoring station, 2021. Retrieved from the EPA Water Quality Portal on 2026-08-02.
Collected and reported by
- Bureau of Reclamation
1119USBR_WQX3 samples · 2021
Analytical methods
- Phosphorus by Single Reagent Colorimetry
- 10200 H ~ Chlorophyll a-b-c Determination
- Turbidity by Nephelometry
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.