 Gibraltar Dam completely blocked migrating steelhead to the upper third of the Santa Ynez River when completed in 1920.This was despite a 1916 suggestion of the California Fish and Game Commission that a fish ladder be constructed with the dam; no such structure was ever built.The dam "altered downstream hydrology, sediment transport, stream habitat, [and] water quality" and also delayed steelhead migration during the early rainy season by holding back floodwaters that otherwise might have breached the sandbar at the mouth of the river.