Only relatively small craft are capable of passing the harbor channel. A large natural sandspit, augmented by breakwaters, protects the harbor from the Pacific Ocean to the west. At its northern end, remains of a bridge that used to connect the shore with the sandspit can be seen. Morro Bay Harbor's channel silts up and must be dredged every three to four years. Previously, the Shark Inlet connected the back bay to the ocean. Some have proposed reopening it to slow the sedimentation that is filling up the bay. There has also been work on reducing erosion in the Chorro Creek watershed to reduce the amount of sediment coming into the bay to form bottom layers of bay mud. Chorro Creek is the bay's largest tributary. It forms an estuary in the back bay between Morro Bay and Los Osos. The second largest tributary, and the only other significant one, is Los Osos Creek, which empties into the far south end of the back bay.