A dam was built across this canyon, flooding it to create Upper Oso Reservoir, which now forms the headwaters of the creek, fed by three small seasonal streams.

After leaving the reservoir, Oso Creek crosses under California State Route 241 and for the next mile (1.6 km) of its course, it flows through a narrow riparian corridor surrounded by residential areas in the city of Mission Viejo.

It then bends slightly to flow southwest and enters a culvert under Marguerite Parkway, emptying into another golf course, 8 miles (13 km) from the mouth.

It passes the Galivan Basin, which functions to capture floodwaters from Oso Creek, on the right bank, and receives from the right a second unnamed tributary, 7.5 miles (12.1 km) from the mouth.

[2][3][4] The creek then bends southwest around several shopping centers near the convergence of Interstate 5 and California State Route 73, within the city limits of Laguna Niguel.

Near this area, Oso Creek enters a concrete flood control channel with sloping sides, 5 miles (8.0 km) from the mouth.

The creek then spills out into a natural channel, 1.2 miles (1.9 km) from the mouth, which it has incised to depths of 50 feet (15 m) or more, as the interstate bends southeast.

[5] The southernmost portions of the San Joaquin Hills lie to the west and southwest of the Oso Creek watershed, and the Santa Ana Mountains border it to the north and northeast.

A structure exists on Oso Creek that is designed to divert a portion of the flow into the Galivan Basin depending on the specific level of a high inflow.