There are a number of tidal channels in Biscayne National Park. They can occur between islands or between shoals, and are especially abundant at the north end of the park in the area known as "The Safety Valve." Channels are a mixture of Bay and ocean water, affected by the ebb and flow of tides. There is regular turbulence and abundant food and oxygen supply with a salinity similar to the open ocean. Shoals are shallow areas with plenty of sunlight, frequent turbulence, current flow, and dense colonies of algae.