At Eel River dam, thousands of spawning lamprey make for natural spectacle

The Press Democrat

Swimming by the thousands up the Eel River this year, Pacific lamprey are literally climbing the wall of a dam near Potter Valley in Mendocino County.

Driven by the biological imperative to spawn in the river’s gravel beds, the snake-shaped, prehistoric fish — commonly mistaken for eels — have almost no chance of scaling the 63-foot high Cape Horn Dam.

For decades, their best option has been a fish ladder that flanks the dam, but even it halts the migratory journey for most lamprey, a largely ignored ocean-going species that shares the stream with federally protected chinook salmon and steelhead trout. Those that do clear the passage, by inching their way up the concrete walls, take up to five weeks to do so.

 “They go crazy at night just trying to find a way up,” said Scott Harris, a Department of Fish and Wildlife biologist who runs the Van Arsdale Fisheries Station next to the dam.