The creek is home to pond turtles, red-legged frogs, tiger salamanders, birds of all kinds, and several species of fish. The creek also contains what may be the last steelhead run in the South Bay . Steelhead are seagoing trout that return to their place of birth to spawn. As steelhead work their way up San Francisquito, their greatest obstacles are diversion dams. In 1995 a fish ladder was built over the Felt Lake diversion dam on Los Trancos Creek, allowing steelhead to spawn in the upper watershed.
Pollution is another major threat to the creek .
In addition to the garbage that is abundant in certain stretches, pollutants such as oil enter San Francisquito from storm drains. Many people are unaware that runoff from our streets is not processed through the sewer system , but instead enters our creeks directly. Manure from horse stables in the hills and silt from agriculture and construction are also degrading the water quality of San Francisquito. Perhaps the biggest threat to San Francisquito is construction too close to its banks. To protect their property interests, many nearby residents have built cement walls along the creek to prevent its banks from collapsing.