Although wetlands make up only about 4% of the Bay watershed, these 1.5 million acres of habitat serve essential functions in the ecosystem, including acting as water filters, providing flood and erosion control, and providing habitat for fish and wildlife. Changes along the coast and pressures from increasing human populations—more than half the population of the United States lives in coastal counties—are causing the loss of wetlands. Since the 1700s, more than half of all the wetlands in the lower 48 states have been lost. Within the Chesapeake Bay, more than 60% of the historic wetlands no longer exist. In the Bay watershed, where so much of the land is in direct contact with a stream, river, or the main stem of the Bay, population growth and associated development place enormous pressures on existing natural resources. These pressures particularly affect wetlands, which are highly vulnerable to changes in water flow and pollution. The good news is that the rate of coastal wetland loss has declined over the past decades, particularly for tidal coastal wetlands such as salt marshes. Federal and state regulations governing the destruction of wetlands are partly responsible, as are community efforts to preserve existing coastal wetlands and restore damaged areas. In recent years, citizens, organizations, and state and federal governments have begun to work together to protect, restore, and create valuable wetland habitats.