Madison River Drought Management

Our operations on the Madison River

Map of Hebgen and Ennis Lakes and the Madison River

Our operations on the Madison River

Hebgen is a storage reservoir and provides many benefits, including recreation and fish habitat. It also supports irrigation and electric generation downstream.

Hebgen Dam does not produce energy. We use Hebgen Dam to manage flows downstream for the Madison River fishery and Ennis Lake elevations.

Ennis Lake elevations are controlled by Madison Dam, which produces power. Madison Dam was recently upgraded a 12-megawatt facility, up from 8 megawatts. 

Low snowpack could make for challenging water year in 2024

NWCC Map showing that most river basins are below normal for snowpack

Low snowpack could make for challenging water year in 2024

March has started off strong with some much-needed snow around the Madison basin. Snowpack is still below the median, but trending in the right direction. 

Hebgen Dam releases to the Madison River are being held at minimum volumes (825 cfs) to provide for FERC license minimum flows below Madison Dam and to protect incubating eggs in brown trout redds (spawning nests in gravels).


As of mid-February, the four SNOTEL sites above Hebgen (Black Bear, Madison Plateau, Whiskey Creek, and West Yellowstone) are at 87% of the 30-year median. In an average water year, peak SWE (snow water equivalent) levels above Hebgen typically occur by April 15. After this point, while there may still be occasional snowstorms, the focus shifts from building snowpack to the transition into runoff.

Runoff Forecasts

April runoff forecasts from NRCS are showing April-July runoff to be 89% of normal or lower. April-July months are very critical months to forecast as this water is the main source of filling the reservoir. NRCS runoff forecast table shows April-July 50% exceedance at 310 KAF (Thousand Acre-Feet). Inflows for these months could be similar to those in recent years, including 2021, 2016 and 2013.


Snowpack report

(As of Thursday, April 11, 2024)

Station NameSnow Water Equivalent (in)

Median Snow Water Equivalent (in) (1991-2020)

Snow Water Equivalent % of median (1991-2020)
Black Bear33.238.686
Madison Plateau20.523.288
West Yellowstone8.2991
Whiskey Creek13.814.893


Weather Forecast

NOAA map show a precipitation outlook that is below normal.

Weather Forecast

Both the short-term and long-term forecast are showing above-normal temperatures and below-normal precipitation.

Northwestern Energy will continue to monitor the snowpack conditions throughout the remaining winter and spring, but if things continue in this trend, it could be another challenging water year.

Managing water temperatures to protect the fishery

fly fisherman

Managing water temperatures to protect the fishery

In the summer, we provide pulse flows out of Hebgen Lake into the Madison River below Ennis Lake. Our pulse flow program is designed to maintain lower Madison River temperatures at or below 80 degrees in order to prevent fish mortality caused from elevated water temperatures.

The Madison Thermal Decision Support System (DSS) was developed to protect fisheries and other river resources.

Madison-Hebgen Stakeholder Engagement Process

Our Federal Energy Regulatory Commission (FERC) license outlines how we manage flows in the Madison River and lake elevations at Hebgen and Ennis reservoirs. It specifies flow requirements at several locations on the river and elevation requirements for both Hebgen and Ennis reservoirs. NorthWestern’s goal for managing water in the Madison is to balance the resources relying on the water provided from Hebgen Reservoir including recreation, fisheries, water temperatures and power production downstream all while operating within our FERC license requirements.

However, in drought years, such as 2021, there are times we cannot meet the flow requirements while also maintaining minimum lake elevations. There simply isn't enough water. During these low water times, we work FERC, Montana Fish Wildlife & Parks, the U.S. Forest Service, the U.S. Fish & Wildlife Service and other regulatory agencies to determine the best management for the limited amount of water we have.

In addition to consulting with FERC and the resource agencies, NorthWestern initiated the Madison Stakeholder Engagement Process in summer of 2022. The purpose of the engagement process is to gather and exchange information among those directly affected by river flows and reservoir levels, agencies responsible for fisheries and recreation management, and NorthWestern Energy. The benefit of the process will be a greater understanding of issues and challenges of operating during times of limited water availability.

Madison-Hebgen: Stakeholder Engagement Process

Download the presentation from our June 22, 2022 meeting.

Madison Drought Impact Study

NorthWestern works diligently to meet its FERC obligations and is committed to fulfilling its responsibilities at the Hebgen Development. Those responsibilities at Hebgen are numerous and complex.

How drought conditions impact our operations:

  • Forecasts and modeling are closely followed by NorthWestern Energy to manage releases to the Madison River downstream and to capture and fill Hebgen Reservoir in the spring.
  • Limited snowpack and spring precipitation create challenging conditions to fully fill Hebgen reservoir while providing required flows to the Madison River.
  • Water releases from Hebgen reservoir feed Ennis Reservoir to support pulsed flow releases out of Madison Dam.
  • The pulse flows are calculated using a model that helps determine the volume of water to be released, allowing for the conservation of water while maintaining safe water temperatures in the lower Madison River.
  • Low flows directly affect the amount of electricity generated at Madison Dam. 
  • NorthWestern Energy’s stewardship responsibilities of the river resources include balancing the many interests of multiple stakeholders.
  • The cooperation and flexibility of all help to protect and maintain the long-term health of the river system, which is our priority.