 From its sources in the Glen Canyon , the entire creek stretched about 3 @.@ 5 miles ( 5 @.@ 6 km ) to the San Francisco Bay . The mouth was nearly 2 miles ( 3 @.@ 2 km ) wide , providing up to 85 % of the drinking water in San Francisco . Due to urban development , however , the watershed of Islais Creek has been reduced by roughly 80 % from its historical extent . A large number of neighborhoods in San Francisco today , such as <unk> Heights , Hunters Point , <unk> Valley , parts of the Mission and <unk> Hill , was once covered by the extent of the creek . 
