NorthWestern Energy/Avista Colstrip Agreement

NorthWestern Energy will acquire Avista’s 222-megawatt ownership of Colstrip Units 3 & 4 in 2026.

NorthWestern Energy and Avista entered into an agreement to provide NorthWestern Energy’s Montana customers needed on-demand power generation capacity and allow Avista to exit ownership of the Colstrip plant in accordance with the state of Washington laws. 

  • NorthWestern Energy will acquire Avista’s ownership of Colstrip Units 3 & 4, 222 megawatts, with no purchase price, effective on Jan. 1, 2026.
  • Avista will retain its obligation for its portion of environmental and decommissioning costs associated with the future closure of the plant.
  • NorthWestern Energy will be responsible for operational costs for the 15% shares of Colstrip Units 3 & 4 when ownership is transferred.
  • Avista and NorthWestern Energy will prorate Avista’s share of the cost of certain capital expenses for the Colstrip plant from now through Jan. 1, 2026.
Brian Bird speaks at a Montana Chamber of Commerce event

“More resources that can generate power on-demand, 24/7, located in Montana and dedicated to serve Montanans, are needed to meet our responsibility to provide our customers with reliable energy service, keep them safe in all weather conditions and avoid an energy crisis.” 

Brian Bird

NorthWestern Energy President and CEO


Why are we acquiring Avista's ownership of Colstrip?:

  • Acquiring more generation at no purchase price allows NorthWestern Energy to continue to make other necessary investments in our Montana energy system with less impact on customers’ bills.
  • It is impossible to identify, permit and build a new resource to meet our Montana customers’ needs that is capable of the same on-demand, 24/7 generation in that timeframe.
  • Any new resource would cost about $500 million to build.
  • In addressing the need for additional on-demand, 24/7 generation in Montana to avoid an energy crisis, NorthWestern Energy continues to implement our “all-of-the-above” strategy to meet our customers’ energy needs. 

Colstrip's role in extreme weather

pie chart showing the resource output from Dec 21-23, 2022.

Colstrip's role in extreme weather

  • During frigid temperatures in December 2022, 41% of NorthWestern Energy’s peak Montana energy load was met with market purchases, primarily from out of state, and most at extremely high prices.
  • NorthWestern Energy’s Montana natural gas-fired generation facilities, share of the Colstrip plant and hydro generation supplied about half of the power during our customers’ highest energy need.
  • Weather conditions, including the extreme cold temperatures, meant NorthWestern Energy’s considerable Montana wind generation resources could not provide much, if any, power.
Transmission lines in Colstrip, Montana.

Had this incremental share of Colstrip and the Yellowstone County Generating Station been available to NorthWestern Energy during the Dec. 21-23, 2022 extreme cold, it would have saved our customers millions of dollars in energy costs procured from out-of-state providers. We have a responsibility to reduce that level of risk to reliable energy service for our Montana customers. 

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A step toward net zero emissions

Learn how the Yellowstone County Generating Station and Colstrip are helping us reach our net zero emission goals.

Our Balanced and Diverse Energy Mix

A chart showing our resource mix

Our Balanced and Diverse Energy Mix

At NorthWestern Energy, our goal is to provide our customers reliable energy at the lowest long-term cost. We do this through a balanced mix of safe, reliable, affordable and clean energy. Our electric portfolio is built on the carbon-free hydro system, along with wind, coal, gas and solar.

Over time, the natural gas plants and other thermal generation on our system will be used less as new cleaner, cost‑effective resources are available.

For more information about the project, please contact: