Reservoir · Idaho · United States · BOR RISE
Arrowrock Reservoir
Arrowrock Reservoir and Dam
25.8% full
Capacity
335.78 hm³
Volume stored
87 hm³
Coordinates
43.595°N, 115.923°W
Last updated
2026-09-30
Current fill
25.8%vs 7 days ago
-2.6%losing
vs 1 year ago
-2.6%year-over-year
7-day trend
↓falling
Data source: BOR RISE — US Bureau of Reclamation — daily reservoir storage volume. Capacity is the design (normal full-pool) capacity from the US National Inventory of Dams (NID); fill % = current volume ÷ design capacity. Last reading: 2026-09-30.
Catchment Weather
Past 30 days + 14-day forecast · Open-Meteo
Satellite imagery: Esri, Maxar, Earthstar Geographics. Map: Esri, HERE, Garmin, © OpenStreetMap contributors. 43.595, -115.923 · Open in Google Maps
About Arrowrock Reservoir
As of September 30, 2026, Arrowrock Reservoir is filled to 25.8% of its total capacity, holding roughly 87 hm³ of water out of a maximum 336 hm³. At this level the reservoir is low.
Over the most recent week on record the fill level has fallen by 2.6 percentage points, and it is 2.6 points below its level on the same date a year earlier.
Across the readings we hold for Arrowrock Reservoir — 2187 data points between October 2, 2021 and September 30, 2026 — the level has ranged from a low of 16.4% (October 2, 2021) to a high of 98.9% (April 17, 2026). On average the reservoir is fullest around June and at its lowest around October.
It is operated by BOR primarily for multiple purposes. It lies within the Idaho basin at 43.595°N, 115.923°W.
Key facts
- Current fill level
- 25.8%
- Water stored
- 87 hm³
- Total capacity
- 336 hm³
- 7-day change
- ▼ 2.6 pts
- Year-on-year
- ▼ 2.6 pts
- Primary use
- Multipurpose
- River basin
- Idaho
- Operator
- BOR
- Coordinates
- 43.595°N, 115.923°W
- Last updated
- September 30, 2026
Recent readings
| Date | Fill level | Volume (hm³) |
|---|---|---|
| 30 Sep 2026 | 25.8% | 87 |
| 29 Sep 2026 | 25.6% | 86 |
| 28 Sep 2026 | 25.6% | 86 |
| 27 Sep 2026 | 26.2% | 88 |
| 26 Sep 2026 | 27.7% | 93 |
| 25 Sep 2026 | 28.6% | 96 |
| 24 Sep 2026 | 28.5% | 96 |
| 23 Sep 2026 | 28.4% | 95 |
| 22 Sep 2026 | 28.3% | 95 |
| 21 Sep 2026 | 28.1% | 94 |
| 20 Sep 2026 | 28.0% | 94 |
| 19 Sep 2026 | 27.9% | 94 |