Both Rock and Richardson Creeks have populations of anadromous and resident salmonids, as well as a number of other fish species. While these populations are small and localized they are regionally unique within an urban growth boundary and in an urbanizing area. Moreover, coho is a candidate species for listing under the ESA, and it is critical to protect all existing habitats. Distribution of Fish Both natural and human barriers limit the distribution of salmonids. In Rock Creek a 20 foot waterfall lies about six tenths of a mile upstream of the creek mouth.
Anadromous fish make use of the area below the falls for spawning and rearing.
In-stream barriers in lower Rock Creek may inhibit movement during low flow periods. Two small tributaries below the falls also provide some limited habitat, although culverts just upstream block these. In middle Rock Creek, resident cutthroat trout have been found in a stretch of the mainstem between Foster Road and SE 172nd Avenues. These fish may be hemmed in by culvert blockages both upstream and down. Lower Richardson Creek anadromous and resident salmonid populations range from the mouth of the Creek up one and a half to two miles.