There are a number of ways for a road to cross a river or stream. These include bridges, fords, open-bottom or arch culverts, box culverts, and pipe culverts. Depending on the type of crossing, its size, method of installation, and maintenance, a road crossing may have many or relatively few adverse impacts on a river or stream ecosystem.
The movement of organisms within rivers and streams is an important ecological process that can be significantly affected by road crossings. There are several ways that crossing structures can impede or prevent the movement of animals: