In physical geography, a wetland is an environment "at the interface between truly terrestrial ecosystems and truly aquatic systems making them inherently different from each other yet highly dependent on both" (Mitsch & Gosselink, 1986). In essence, wetlands are ecotones. Wetlands are typically highly productive habitats, often hosting considerable biodiversity and endemism. In many locations such as the united kingdom and USA they are the subject of conservation efforts and biodiversity action plans.
The united states Army Corps of Engineers and the environmental protection agency jointly define wetlands as: "Those areas that are inundated or saturated by surface or ground water at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions."