New York City once contained 224,000 acres of freshwater wetland. This valuable ecosystem can slow erosion, prevent flooding by retaining storm waters, filter and decompose pollutants, and slow global warming by converting carbon dioxide into oxygen at a prodigious rate. In the past 200 years, the increasing demands of a growing metropolis have resulted in most of this land being filled for construction, or dredged for transport. Only 2,000 acres of freshwater wetland remain in the city today, and many species that once called the wetland home have been lost forever.