Prefumo Creek is a tributary stream of San Luis Obispo Creek. Its mouth is at its confluence with San Luis Obispo Creek at an elevation of 102 feet (31 meters). Its source is found at 35°15′41″N 120°45′28″W / 35.26139°N 120.75778°W / 35.26139; -120.75778 in the Irish Hills. From its source it flows down into Laguna Lake at 35°15′51″N 120°41′32″W / 35.26417°N 120.69222°W / 35.26417; -120.69222, and provides the overflow channel from the lake at 35°15′35″N 120°41′01″W / 35.25972°N 120.68361°W / 35.25972; -120.68361 that drains to the San Luis Obispo Creek.

35°14′40″N 120°40′52″W / 35.24444°N 120.68111°W / 35.24444; -120.68111