The Ballona Wetlands receive water from multiple sources: the ocean, Ballona Creek, rainfall, groundwater, and runoff from adjacent lands. The presence or absence of each of these sources in different areas of Ballona, and varying degrees of human impacts, have significantly affected the kinds of habitats we see. For example, willows along the bluffs are dependent on fresh water, and represent a mere fragment of Centinela Creek that used to flow along the base of the bluffs before surface water was diverted into Ballona Creek.
Ballona Creek was also a major source of fresh water into the wetlands. And like Centinela Creek, Ballona Creek was diverted from the wetlands and confined to a concrete flood control channel. These diversions of freshwater flow, combined with changes in elevation brought about by dumping of dredge material from construction of Marina del Rey and Ballona Creek, have left parts of Ballona dependent only on rainfall as a water source.
For this reason, the plant life observed in these upland areas tends to vary simply with soil type (how much clay or sand is present), and how much the fill has settled over time, rather than by the naturally complex, dynamic interplay of creek flow and tides that existed prior to human impacts. One exception is the Ballona Dunes, now confined to a narrow strip of land between coastal development and the remnant Ballona salt marsh. The Dunes are not on artificial fill, but are dependent on rainfall and the efforts of Friends of Ballona Wetlands to maintain native habitat. Natural forces of wind and water, which shaped the dunes historically, have been lost. This situation is unlikely to change in future due to constraints of adjacent development and roads.
At the heart of the Ballona Wetlands is the coastal salt marsh or estuary, the crown jewel of current restoration planning. Coastal salt marshes depend on disturbance from tides and floods in order to thrive. Under natural conditions, tidal movements -- along with variations in freshwater flow coming from the land -- create complex, ever-changing environmental gradients of topography, moisture, temperature, and salinity that enable many kinds of organisms to find their own particular place. As a result, coastal salt marshes are one of the most biologically diverse and productive habitats in the world.
Adding to the conservation urgency of coastal marshes in southern California is the fact that they are inherently small and therefore most vulnerable to human disturbance. Even in the absence of urbanization, there would be limits to how far the marshes could extend inland before being blocked by mountains – this limitation does not exist in many other parts of the world, where flat coastal landscapes and associated marsh lands extend inland for many miles (historically, at least). For this reason, restoration planning at the Ballona Wetlands is focused on restoring the coastal marsh ecosystem as much as possible, given existing constraints of development, roads, and utility corridors.