Date: Sep 20, 2022

GREAT FALLS, MT -Sept. 20, 2022 -On Sept. 25 NorthWestern Energy will begin drawing down Rainbow Reservoir about 11 feet from the current full-pool level to replace wooden flash boards on the face of the dam.

"The wooden flash boards were last replaced in 2004," said NorthWestern Energy Hydro Plant Foreman Dereck Besich. "The aged boards are leaking water which requires a high level of maintenance and frequent repairs. Replacing the boards will reduce maintenance and make the dam perform more efficiently."

The reservoir water drawdown will begin Sept. 25. Over the next five days the construction project will involve removing old boards and replacing with new ones. The reservoir will be back to full pool by Oct. 6.

People and pet should not enter the riverbed. Deep mud, slippery rocks and the short duration of the water drawdown will create safety hazards.

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About NorthWestern Energy (Nasdaq: NWE)

NorthWestern Corporation, doing business as NorthWestern Energy, provides essential energy infrastructure and valuable services that enrich lives and empower communities while serving as long-term partners to our customers and communities. We are working to deliver safe, reliable, and innovative energy solutions that create value for customers, communities, employees, and investors. This includes bridging our history as a regulated utility safely providing low-cost and reliable service with our future as a globally-aware company offering a broader array of services performed by highly-adaptable and skilled employees. We provide electricity and / or natural gas to approximately 753,600 customers in Montana, South Dakota, Nebraska and Yellowstone National Park. We have provided service in South Dakota and Nebraska since 1923 and in Montana since 2002. More information is available on the company's Web site at www.northwesternenergy.com.

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