With the Glen Canyon site out of the question, the initial need for a reservoir was realized in 1936 with the completion of Hoover Dam in Black Canyon, storing in the mammoth reservoir of Lake Mead. However, it was not able to weather the worst floods or droughts, and was filling with sediment at a rate that would render it useless in a few hundred years. But most importantly, Hoover only controlled the lower portion of the river. The Upper Basin states, whose rivers remained undammed, had no way to ensure they could fulfill their delivery obligation to the Lower Basin state while retaining enough water for their own use. Without storage reservoirs of their own, the Upper Basin states risked a "call" on the Colorado River during drought years: they would be forced to use less water in order to keep the river flowing to Lake Mead and California, the state with the most senior water rights.