Main rivers are a statutory type of watercourse in England and Wales and are usually larger streams and rivers. A main river is defined as such on the Environment Agency’s 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. See our Flood Risk Map for a list of all Northamptonshire main rivers.