I'm not sure of the species, but as a kid (~30 years ago) there used to be large runs of lampreys every summer in Silver Creek. There were at times hundreds of them in a given stretch of the creek. It has been close to 20 years since I've seen an adult. I came across a few juveniles while snorkeling in a different creek (the Abiqua) a few years ago, but only the one time. Their demise seems to have coincided with the decline of salmon runs in the creeks. As a kid they kind of freaked us out, but now I miss them...