Wetland

Wetlands are not only marshes and swamps. A wet meadow, a wooded area that stays soggy into early summer, or a low corner of a pasture can all be wetlands. Scientists identify them by three things together: water at or near the surface for part of the growing season, plants adapted to it, and hydric soils.

The best-known map is the U.S. Fish and Wildlife Service’s National Wetlands Inventory, drawn mostly from aerial imagery. It is a valuable first signal and a poor final answer: it misses some wetlands, maps others that are no longer wet, and draws edges at a scale that can be off by tens of feet.

Why it matters

Filling or building in a wetland can need a federal or state permit, and some will never be approved. Whether a particular wetland is regulated is a separate legal question — see jurisdictional wetland. A mapped wetland across the only dry building site is one of the most common ways a good-looking parcel turns out not to work.