Grassy Lake dam
Grassy Lake
Grassy Lake, located in Teton County, Wyoming, is a Federal-owned reservoir with a primary purpose of irrigation. Built in 1938, this Earth-type dam stands at a height of 118 feet and has a storage capacity of 16,210 acre-feet. The dam spans 1,170 feet and is regulated by the Bureau of Reclamation, ensuring proper inspection, permitting, and enforcement measures are in place to maintain its structural integrity.
With a hazard potential classified as high, Grassy Lake is under regular inspection and monitoring to assess its condition and potential risks. While the dam has undergone modifications in 2005 for hydraulic and structural improvements, its spillway type remains uncontrolled. The reservoir's drainage area of 12 square miles feeds into the Grassy Creek, with a maximum discharge capacity of 675 cubic feet per second.
As a vital water resource for irrigation in the region, Grassy Lake serves as a testament to the careful management and regulation of water infrastructure by the Bureau of Reclamation. Its historical significance, combined with its ongoing risk assessment and management efforts, make it a focal point for water resource and climate enthusiasts seeking to understand the intersection of infrastructure development and environmental stewardship in the American West.
Dam data reference
Condition Assessment
- Satisfactory
- No existing or potential dam safety deficiencies are recognized. Acceptable performance is expected under all loading conditions (static, hydrologic, seismic) in accordance with the minimum applicable state or federal regulatory criteria or tolerable risk guidelines.
- Fair
- No existing dam safety deficiencies are recognized for normal operating conditions. Rare or extreme hydrologic and/or seismic events may result in a dam safety deficiency. Risk may be in the range to take further action.
- Poor
- A dam safety deficiency is recognized for normal operating conditions which may realistically occur. Remedial action is necessary. POOR may also be used when uncertainties exist as to critical analysis parameters which identify a potential dam safety deficiency.
- Unsatisfactory
- A dam safety deficiency is recognized that requires immediate or emergency remedial action for problem resolution.
- Not Rated
- The dam has not been inspected, is not under state or federal jurisdiction, or has been inspected but, for whatever reason, has not been rated.
Hazard Potential Classification
- High
- Dams assigned the high hazard potential classification are those where failure or mis-operation will probably cause loss of human life.
- Significant
- Dams assigned the significant hazard potential classification are those dams where failure or mis-operation results in no probable loss of human life but can cause economic loss, environmental damage, disruption of lifeline facilities, or impact other concerns. Significant hazard potential classification dams are often located in predominantly rural or agricultural areas but could be in areas with population and significant infrastructure.
- Low
- Dams assigned the low hazard potential classification are those where failure or mis-operation results in no probable loss of human life and low economic and/or environmental losses. Losses are principally limited to the owner's property.
- Undetermined
- Dams for which a downstream hazard potential has not been designated or is not provided.
Plan around the weather
Same NOAA / yr.no feed Snoflo's iOS app uses. Watch the precipitation column on the meteogram -- rain on the basin upstream typically lifts inflow 24-72 hours later.
Next 5 days, hour by hour
Temperature line with weather symbols on top, snow + rain accumulation as columns, humidity as a dotted line.
5-day forecast table
Every 3 hours, broken out across temperature, snow, rain, humidity, and wind. Each cell is colour-coded relative to the column min/max.
| Time | Condition | Temp (°F) | Snow (in) | Rain (in) | Humidity (%) | Wind (mps) | Wind dir |
|---|---|---|---|---|---|---|---|
| Loading detailed forecast… | |||||||
15-day temperature & precipitation
Daily temperatures, snow, and rain projected over the next two weeks.
Nearby streamflow gauges
USGS streamgauges around Grassy Lake -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Snake River Ab Jackson Lake At Flagg Ranch Wy | 4,810 cfs | → |
| Falls River Ab Yellowstone Canal Nr Squirrel Id | 1,410 cfs | → |
| Falls River Nr Squirrel Id | 671 cfs | → |
| Snake River Nr Moran Wy | 1,290 cfs | → |
| Pacific Creek At Moran Wy | 2,590 cfs | → |
| Falls River Nr Ashton Id | 1,300 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near Grassy Lake.
Boat launches
Campgrounds
Fishing spots
Paddle runs
- The Headwaters To The Southern Yellowstone National Park Boundary
- Cave Falls Run
- The Headwaters To The Confluence With Falls River
- The Headwaters To Ends Approximately At Kepler Cascades
- Yellowstone Np To Targhee Nf Boundary
- Badger Creek
More reservoirs
Track Grassy Lake in the Snoflo app
Save this dam as a favorite and get the local NOAA / yr.no forecast plus regional flow context wherever you are.
About Grassy Lake
Where does the data for Grassy Lake come from?
Structural and regulatory data come from the U.S. Army Corps of Engineers' National Inventory of Dams (NID). Weather forecast comes from NOAA / yr.no -- the same feed Snoflo's iOS app uses.
How often is the report updated?
NID structural data refreshes annually as the Corps publishes updated assessments. The weather forecast refreshes throughout the day.
What does the High hazard rating mean?
The Corps of Engineers' hazard potential classification grades probable consequences if the dam fails: High = probable loss of human life; Significant = no probable loss of human life but possible economic loss / environmental damage; Low = no probable loss of human life, only minor economic / environmental losses. See the Dam Data Reference card above for the full definitions.
What's "% of normal"?
The current storage value compared to the historical average storage on this calendar day. 100% = right on average; values above 100% mean above-normal storage (wet year); values below mean below-normal (dry year or drought).
Can I get alerts when storage crosses a threshold?
Yes -- alerts are managed in the Snoflo iOS app. Favorite this dam, set a threshold, and you'll get a push the moment conditions cross.
Other water bodies near here
Snoflo-tracked reservoirs and dams within driving distance of Grassy Lake.