Reservoir · Wyoming · United States · BOR RISE
Grassy Lake and Grassy Lake Dam (GRS)
45.7% full
Capacity
19.08 hm³
Volume stored
9 hm³
Coordinates
44.130°N, 110.819°W
Last updated
2026-07-28
Current fill
45.7%vs 7 days ago
+0.1%gaining
vs 1 year ago
-51.1%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: 2026-07-28.
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 (GRS)
As of July 28, 2026, Grassy Lake and Grassy Lake Dam (GRS) is filled to 45.7% 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 (+0.1 pts), and it is 51.1 points below its level on the same date a year earlier.
Across the readings we hold for Grassy Lake and Grassy Lake Dam (GRS) — 2189 data points between July 31, 2021 and July 28, 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
- 45.7%
- Water stored
- 9 hm³
- Total capacity
- 19 hm³
- 7-day change
- ▲ 0.1 pts
- Year-on-year
- ▼ 51.1 pts
- Primary use
- Multipurpose
- River basin
- Wyoming
- Operator
- BOR
- Coordinates
- 44.130°N, 110.819°W
- Last updated
- July 28, 2026
Recent readings
| Date | Fill level | Volume (hm³) |
|---|---|---|
| 28 Jul 2026 | 45.7% | 9 |
| 27 Jul 2026 | 45.6% | 9 |
| 25 Jul 2026 | 47.6% | 9 |
| 24 Jul 2026 | 49.0% | 9 |
| 23 Jul 2026 | 50.4% | 10 |
| 22 Jul 2026 | 51.8% | 10 |
| 21 Jul 2026 | 53.2% | 10 |
| 20 Jul 2026 | 54.7% | 10 |
| 19 Jul 2026 | 56.0% | 11 |
| 18 Jul 2026 | 57.5% | 11 |
| 17 Jul 2026 | 59.0% | 11 |
| 16 Jul 2026 | 60.5% | 12 |
Frequently asked questions
What is the current water level of Grassy Lake and Grassy Lake Dam (GRS)?
As of July 28, 2026, Grassy Lake and Grassy Lake Dam (GRS) is at 45.7% 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 (GRS) reservoir full?
No. As of July 28, 2026, Grassy Lake and Grassy Lake Dam (GRS) is within its normal operating range at 45.7% of its capacity, so it is not full.
Is the water level at Grassy Lake and Grassy Lake Dam (GRS) rising or falling?
The level at Grassy Lake and Grassy Lake Dam (GRS) has been broadly stable over the latest week on record (+0.1 points).
How much water can Grassy Lake and Grassy Lake Dam (GRS) hold?
Grassy Lake and Grassy Lake Dam (GRS) has a total capacity of 19 hm³.
Where is Grassy Lake and Grassy Lake Dam (GRS) reservoir located?
Grassy Lake and Grassy Lake Dam (GRS) 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 (GRS) used for?
Grassy Lake and Grassy Lake Dam (GRS) is used primarily for multiple purposes, and is managed by BOR.