Coastal wetlands are low-lying areas of land that are frequently and regularly inundated with fresh and/or ocean water. How much water they receive, the source of that water, as well as the elevation, slope, and sediment have profound effects on the presence and distribution of vegetation and wildlife. Coastal wetlands are renowned for their ability to capture sediment, withdraw nutrients, slow the flow of water, and through a mixture of habitats, within them, support a great diversity of wildlife.
Most coastal wetlands in Santa Monica Bay are found near the mouths of canyons along the Santa Monica Mountains in Malibu. These ‘lagoons’ are often closed to the ocean in the summer and open when winter rains breach the beach. Trancas, Zuma, Malibu, and Topanga lagoons are some of the most prominent along this section of the coast. In the middle of the Bay where the land is flatter the water used to spread out more, and this led to a large complex of salt and freshwater marshes, mudflats, salt pans, and open water. Much of this coastal wetland was lost to changes in water flows, and urban development. A remnant of that once expansive system is the Ballona Wetlands Ecological Reserve.