 No reliable estimates have been made of the steelhead population prior to Gibraltar's construction; however, it is believed to have been much greater.The dam did not appear to have a large impact on downstream steelhead populations; in 1946 a group of fisheries biologists described steelhead habitat between Solvang and Gibraltar Dam as "excellent".Steelhead migration to the base of Gibraltar Dam ended with the completion of Bradbury Dam in 1953.