Toutle River

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Mouth of the Toutle River in flood near Castle Rock, Washington. Photo taken prior to the 1980 eruption of Mt. St. Helens.

North Fork Toutle River valley filled with sediment

Dredging the Toutle River of volcanic ash

The sediment retention structure on the North Fork of the Toutle River

The Toutle River is a river in southwestern Washington State, in the Pacific Northwest region of the United States. It rises on the flanks of Mount St. Helens and joins the Cowlitz River near Castle Rock.

[edit] Eruption of Mt. St. Helens

The May 18, 1980 eruption of Mt. St. Helens and subsequent lahars poured vast amounts of sediment into the Toutle, which was formerly navigable. The US Army Corps of Engineers dredged 85 million m³ (110 million yd³) of sediment from the river and built the US$65 million Sediment Retention Structure on the North Fork of the Toutle to keep it clear in the future. Part of the same engineering works is a tunnel to drain Spirit Lake whose natural outlet was blocked by the eruption.