The Los Angeles and San Gabriel Rivers both originate in mountainous
areas including a large portion of the Angeles National Forest. They
flow through the mountains into the San Fernando and San Gabriel Valleys,
both of which are underlain by rich groundwater basins. The rivers
then continue on over the coastal plain of Los Angeles into the Los
Angeles/Long Beach Harbor and into the Pacific Ocean.
Due to pressures of urbanization both rivers have been highly modified
with dams and concrete channeling resulting in a loss of habitat and
human access to the rivers. Diversions of water for use in groundwater
recharge, significant discharges of wastewaters including sewage treatment
plant reclaimed waters, and non-point source contributions such as
urban runoff have dramatically changed the natural hydrology of the
rivers. The watersheds are host to a wide range of wildlife species
(especially in the upper more pristine areas), many of which are now
listed on federal and state endangered and threatened species lists.
