St. Marys Lake dam
St. Marys Lake
St. Marys Lake, also known as Geo. R. Stewart Reservoir, is a privately owned water resource located in Idaho Springs, Colorado. This reservoir was completed in 1889 and primarily serves as a water supply source for various purposes including fire protection, stock, irrigation, and small fish pond maintenance. With a storage capacity of 51 acre-feet, St. Marys Lake covers a surface area of 7 acres and has a maximum discharge rate of 220 cubic feet per second.
Despite its historical significance and critical role in water management, St. Marys Lake poses a significant hazard potential with an unsatisfactory condition assessment. The dam, standing at a height of 9 feet and a length of 210 feet, has an uncontrolled spillway type with a width of 40 feet. The risk assessment for this reservoir is classified as moderate, highlighting the need for ongoing risk management measures and regular inspections to ensure public safety and environmental protection. As a key component of the water infrastructure in Clear Creek County, St. Marys Lake requires careful monitoring and maintenance to mitigate potential risks and ensure sustainable water resource management for the future.
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 St. Marys Lake -- inflows here typically show up in storage 24-72 hours later.
| Streamgauge | Discharge | View |
|---|---|---|
| Clear Creek Near Lawson | 128 cfs | → |
| Moffat Water Tunnel At East Portal | 249 cfs | → |
| West Fork Clear Creek Abv Mouth Nr Empire | 55 cfs | → |
| Clear Creek Abv West Fork Clear Creek Nr Empire Co | 78 cfs | → |
| Fraser River At Upper Sta | 25 cfs | → |
| Fall River Near Idaho Springs | 10 cfs | → |
Make a day of it
Boat launches, lakeside camping, fishing access, and other reservoirs near St. Marys Lake.
Boat launches
- Miramonte Road Boulder County
- Fairway Drive Evergreen
- Ralston Creek Trail Arvada
- Cr 6 Grand County
- Willow Creek Boating Site
- Us 34 Grand County
Fishing spots
Paddle runs
- Upper South Boulder Creek
- Upper Clear Creek
- Tunnel 1 To Golden Whitewater Park
- Golden Whitewater Park
- Lower Boulder Canyon
More reservoirs
Track St. Marys 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 St. Marys Lake
Where does the data for St. Marys 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 Significant 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 St. Marys Lake.