1968 300mw Mossyrock Dam on Cowlitz River creates Riffe Lake near Mount Rainier, WAS

(Satellite)

Dec 2025 Flood

Dec 15, 2025:

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Four days later, they still are not using the fourth gate.

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Keith Carrol, Jul 2020

This double curvature arch dam is 365' [111m] above riverbed and 606' [185m] above bedrock. [mytpu]

Each unit is 150mw.

8:14 video @ 9:45
Learn about how we rebuilt the Mossyrock powerhouse generators.

This video must have been taken around 2010. The lake level was lowered in 2017 because seismic issues were discovered. It will be at least until 2031 before they can fix the issues and restore the lake level. [mytpu_whoops] In the meantime, they can't make full use of those new generators.

@ 8:14

I wonder if the Dec 2025 rains would have caused serious problems if the lake had not been lowered because of seismic  issues. It is a shame they have to dump the water quickly rather than let it drain through the generators.

The Chronicle posted 0:26 video

Water cascades through three of the Mossyrock Dam's four spillways as Tacoma Power staff slowly drain a swelled Riffe Lake following last week's atmospheric river event.

According to the National Oceanic and Atmospheric Administration's (NOAA) lake level gauge, Riffe Lake's level is currently at 755.93 feet. From Dec. 7 through Dec. 14 during the storms, the level rose from around 720 feet up to almost 760 feet.

Video by Chronicle reporter Owen Sexton.