Reservoir · Wyoming · United States · BOR RISE
Grassy Lake and Grassy Lake Dam
46.1% full
Capacity
19.08 hm³
Volume stored
9 hm³
Coordinates
44.130°N, 110.819°W
Last updated
2026-08-12
Current fill
46.1%vs 7 days ago
+0.2%gaining
vs 1 year ago
-13.8%year-over-year
7-day trend
→stable
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: 2026-08-12.
Catchment Weather
Past 30 days + 14-day forecast · Open-Meteo
Satellite imagery: Esri, Maxar, Earthstar Geographics. Map: Esri, HERE, Garmin, © OpenStreetMap contributors. 44.130, -110.819 · Open in Google Maps
About Grassy Lake and Grassy Lake Dam
As of August 12, 2026, Grassy Lake and Grassy Lake Dam is filled to 46.1% of its total capacity, holding roughly 9 hm³ of water out of a maximum 19 hm³. At this level the reservoir is within its normal operating range.
Over the most recent week on record the fill level has held broadly steady (+0.2 pts), and it is 13.8 points below its level on the same date a year earlier.
Across the readings we hold for Grassy Lake and Grassy Lake Dam — 2187 data points between August 15, 2021 and August 12, 2026 — the level has ranged from a low of 45.6% (July 27, 2026) to a high of 99.8% (June 7, 2022). On average the reservoir is fullest around June and at its lowest around August.
It is operated by BOR primarily for multiple purposes. It lies within the Wyoming basin at 44.130°N, 110.819°W.
Key facts
- Current fill level
- 46.1%
- Water stored
- 9 hm³
- Total capacity
- 19 hm³
- 7-day change
- ▲ 0.2 pts
- Year-on-year
- ▼ 13.8 pts
- Primary use
- Multipurpose
- River basin
- Wyoming
- Operator
- BOR
- Coordinates
- 44.130°N, 110.819°W
- Last updated
- August 12, 2026
Recent readings
| Date | Fill level | Volume (hm³) |
|---|---|---|
| 12 Aug 2026 | 46.1% | 9 |
| 10 Aug 2026 | 46.1% | 9 |
| 8 Aug 2026 | 46.0% | 9 |
| 7 Aug 2026 | 46.0% | 9 |
| 6 Aug 2026 | 46.0% | 9 |
| 5 Aug 2026 | 45.9% | 9 |
| 4 Aug 2026 | 45.9% | 9 |
| 3 Aug 2026 | 45.9% | 9 |
| 2 Aug 2026 | 45.9% | 9 |
| 1 Aug 2026 | 45.8% | 9 |
| 31 Jul 2026 | 45.8% | 9 |
| 30 Jul 2026 | 45.8% | 9 |
Frequently asked questions
What is the current water level of Grassy Lake and Grassy Lake Dam?
As of August 12, 2026, Grassy Lake and Grassy Lake Dam is at 46.1% of its capacity, holding approximately 9 hm³ of water, according to BOR RISE (US Bureau of Reclamation) data.
Is Grassy Lake and Grassy Lake Dam reservoir full?
No. As of August 12, 2026, Grassy Lake and Grassy Lake Dam is within its normal operating range at 46.1% of its capacity, so it is not full.
Is the water level at Grassy Lake and Grassy Lake Dam rising or falling?
The level at Grassy Lake and Grassy Lake Dam has been broadly stable over the latest week on record (+0.2 points).
How much water can Grassy Lake and Grassy Lake Dam hold?
Grassy Lake and Grassy Lake Dam has a total capacity of 19 hm³.
Where is Grassy Lake and Grassy Lake Dam reservoir located?
Grassy Lake and Grassy Lake Dam is located in Wyoming, United States, within the Wyoming basin (coordinates 44.130°N, 110.819°W).
What is Grassy Lake and Grassy Lake Dam used for?
Grassy Lake and Grassy Lake Dam is used primarily for multiple purposes, and is managed by BOR.