Arrowrock Reservoir
Arrowrock Reservoir is managed by U.S. Bureau of Reclamation. Lake Insights displays its latest available elevation from USACE NWW District.
Lake Status
- 7-day trend
- Rising
- 7-day change
- Up 0.71 ft
- 30-day change
- Up 0.71 ft
- Last updated
- Today
Watershed drought conditions
Boise County, ID · surrounding county from lake location
Abnormally Dry
The surrounding county is abnormally dry, which is not official drought.
Severity
Weekly trend
Improving
Compared with last week
Official drought
Yes
19.7% of the watershed is currently classified as official drought (D1+).
U.S. Drought Monitor · map date Sep 8, 2026. Updated weekly. droughtmonitor.unl.eduView drought map for Boise County, ID
Key Facts
Managing authority
Waterbody / project type
Official purposes
Current-level source
Project / NID identifier
Dam / watershed (NID design values)
Static design values from a confidently matched National Inventory of Dams record — not live gage readings.
- Normal storage
- 272,224 acre-ft
- Max storage
- 283,700 acre-ft
- Surface area at normal pool
- 3,256 acres
- Drainage area
- 2,217 sq mi
- Spillway capacity (design)
- 16,080 cfs
- Dam structure
- Concrete · 350 ft high · completed 1915
- Hazard classification
- High
- Safety & inspection
- last inspection May 5, 2021
National Inventory of Dams · matched record: Arrowrock Dam (ID00280)
How this lake is operated
- Documented project purposes (National Inventory of Dams): Flood Risk Reduction, Fish and Wildlife Pond, Irrigation, Recreation, Water Supply.
Why the level can change
General factors for reservoirs like this
These are common influences for this type of lake. They do not identify the cause of a specific current change unless an operator update confirms it.
Rainfall & inflows
Rain and upstream river inflows can raise reservoir levels, especially after storms.
Downstream releases
When an operator releases water through a dam, reservoir storage can fall and downstream flows can rise.
Flood-risk operations
Some projects store or release water under flood-risk rules when conditions require it.
Water supply
Some reservoirs support municipal, industrial, irrigation, or regional water-supply needs.
Hydropower
Hydropower projects may pass water through turbines when generating electricity.
Seasonal weather
Dry periods, heat, evaporation, and seasonal rainfall patterns can affect storage over weeks and months.
Current data source
Managing authority: U.S. Bureau of Reclamation
Observation source used by Lake Insights: USACE NWW District
Who manages the lake and who publishes the reading Lake Insights displays can differ. Lake Insights does not invent a source label from the managing authority alone.
General education
Shared background — not lake-specific facts
Lake Insights aggregates water level information from authoritative public sources such as the U.S. Army Corps of Engineers, NOAA, TVA, Bureau of Reclamation, power utilities, and other official lake operators. We preserve historical observations, calculate trends, and present lake conditions in a consistent format. For USACE NWW District, we link to the official source whenever it is available. Lake Insights does not predict future lake levels unless an official forecast has been published by the managing authority.
Common questions about Arrowrock Reservoir
- Who manages Arrowrock Reservoir?
- Arrowrock Reservoir is managed by U.S. Bureau of Reclamation. Lake Insights reports published gauge readings; it does not operate the waterbody.
- Where does Lake Insights get the level reading for Arrowrock Reservoir?
- Lake Insights displays the latest available elevation for Arrowrock Reservoir from USACE NWW District. The managing authority (U.S. Bureau of Reclamation) may differ from the agency that publishes the observation used on this page.
- What are the documented purposes of Arrowrock Reservoir?
- Documented purposes for Arrowrock Reservoir (National Inventory of Dams): Flood Risk Reduction, Fish and Wildlife Pond, Irrigation, Recreation, Water Supply.