Most of these coastal wetlands are nearly pristine. It is remarkable to go out into the hundreds of thousands of acres of coastal wetlands and see the masses of birds of all types that winter there. Key duck species include northern pintails, green-winged teal, and lesser scaup. Equally remarkable is the realization that these wetlands look and function very much as they have for thousands of years. One has the sense of being in an untouched wilderness. The water is just a few inches deep for thousands of acres. Thick, silty mud lies beneath, making these shallows impassable except by airboat. As a result, beachfront properties and seaports have not been developed. And because no petroleum products are known to be under these wetlands, they have not been threatened by exploration and extraction activities.
Sophisticated irrigated agriculture dominates much of the coastal plain. Irrigation has changed when and how often fresh water flows from the Sierra Nevada Mountains to the wetlands. Agricultural chemicals and fertilizers find their way into the wetlands and inevitably affect water quality. And large volumes of other nutrients come from the expanding human population, which is served by limited sewage-treatment facilities.
Despite these impacts, the wetlands remain nearly fully functional ecosystems, as they have for centuries. Many of the nutrients and chemicals are interrupted by vast acreages of cattail marshes that have formed at the mouths of many rivers and other routes that the irrigation waters follow to the coast. The marshes are natural filters of these pollutants and play a critical role in protecting hundreds of thousands of acres of other coastal wetlands.
In the last decade, a new threat to these coastal wetlands has emerged as the shrimp-farming industry has expanded along the coast. The greatest impact occurs where shrimp farms have been placed in mangrove swamps that are in the transition zone between freshwater and brackish wetlands. These mangrove wetlands not only provide crucial habitat for waterfowl and millions of other birds but are also the nursery habitats for most of the important commercial fisheries that coastal residents depend on for food. One acre of mangrove swamp is the birthplace of what eventually becomes about 1,500 pounds of seafood harvested in the ocean. For this reason alone, countries all over the world are working to restore mangrove wetlands that have been lost to road- and levee-building and the growth of their own shrimp-farming industries.