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

A Montana map showing the snowpack for different river basins, including the Madison river basin, which is 51% of normal.

Low snowpack could make for challenging water year in 2024

As we reach the latter part of winter with not a lot of snow, 2024 could be another challenging water year. The recent precipitation has been beneficial but we continue to see snowpack levels well below the 30-year average.

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 75% of the 30-year median. Based on an average water year, about 60% of the SWE (snow water equivalent) levels should already be established in the mountains by Feb. 10. Therefore, we will need to receive above-normal snow in the next few months to catch up to the 30-year median SWE numbers.

Runoff Forecasts

February runoff forecasts from NRCS is showing April-July runoff to be 70% 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 (see below) shows April-July 50% exceedance at 245 KAF (Thousand Acre-Feet). Inflows for these months could be similar to those in recent years, including 2021, 2016, 2015, 2007, and 2001.


Preliminary Missouri River Basin Forecasts

Forecast PointPeriod50% (KAF)% of med10% (KAF)30% (KAF)70% (KAF)90% (KAF)30-year med
Hebgen Lake InflowApr F-Jul L24570335280210157350
 Apr F-Sep L32070425360275215455


Weather Forecast

A map of the United States showing the seasonal precipitation outlook, including that the oulook for western Montana is below normal

Weather Forecast

The long-term forecast is showing below-normal precipitation and above-normal temperatures. If this forecast holds true, we may see an earlier runoff than normal.

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.