Main rivers are a statutory type of watercourse in
England and
Wales, usually larger streams and rivers, but also include some smaller watercourses. A main river is defined as a watercourse marked as such on a main river map, and can include any structure or appliance for controlling or regulating the flow of water in, into or out of a main river. The
Environment Agency's powers to carry out flood defence works apply to main rivers only. In
England main rivers are designated by
Defra. The
Welsh Government performs this function in
Wales. Every other open watercourse in England and Wales is determined by statute as an '
ordinary watercourse'.