The back bay, roughly anything south of the Morro Bay State Park Marina, is very shallow. However, there is some slightly deeper water in the channels. The largest channel continues from the bay's main channel, winding its way towards Los Osos, on the southern end of the bay. The second largest breaks off from the largest about halfway to Los Osos and takes an extremely windy route to the sandspit. A few small channels on the landward side formed by runoff meet the largest channel as well. The narrow, unmarked channels are very hard to navigate and are filled with eel grass, which can snag the boat or clog the propeller. They are easiest to find at low tide, but if the tide is too low, the boat may run aground because the channels are only a few feet deeper than the surrounding water. An alternative to searching for the channels is to cross at very high tide.