Human activity in California has historically changed the wetlands from one type to another or contributed to its complete loss. It is most often converted to agricultural grounds.
Human activity such as unnatural changes to the hydrological period of flooding in wetlands is another threat to this ecosystem. Many manmade structures such as damns, revetments, and other modifications. Most wetlands in California rely on irrigated water and groundwater pumping.
As in any ecosystem, invasive species are a huge threat as they compete with the native species in the area for limited resources and often times dominate the area overtime, ultimately altering the ecosystem services that the area provides. The Louisiana red crayfish is a good example of an invasive species that has contributed to the decline of native amphibians and fish at Malibu Creek, just about 10 miles north from UCLA.