According to Wydoski and Whitney (1979) spawning occurs in June-July in Washington. In southern California, spawning likely begins by late January in most years, and spawning may continue into April (Chase 2001). Eggs hatch in 2 or 3 weeks. Ammocoetes remain in stream, metamorphose in 4-6 years (late September-October). Form macrostoma in British Columbia: spawns May-August, probably spends 6 years as larva and 2 years as subadult-adult before reproducing; metamorphosis July-October (Beamish 1987). This is the only species of lamprey in which some individuals (from Washington) are known to spawn more than once (Page and Burr 1991).