Mersey, a river of England, formed by the union of several small streams, which have their sources in the hills near the borders of Yorkshire, Cheshire, and Derbyshire. The two principal of these, the Tame and the Goyt, after receiving the waters of all the rest, unite at Stockport. Here the river takes the name of Mersey, and flowing W. divides Cheshire from Lancashire, and falls into the Irish sea below Liverpool. The chief affluents of the Mersey are the Irwell and Weaver. At Runcorn, about 17 m. from its mouth, it expands into a large estuary, which varies in breadth from 2 to 3 m., and contracts at its mouth to about three fourths of a mile. The course of this river is mostly through a level country, but its scenery is occasionally very picturesque. The principal towns on its banks are Stretford, Warrington, Hale, Garston, and Liverpool on the right, and Stockport, Runcorn, Ince, and Birkenhead on the left. Its entire length is from 55 to 60 m., and it is navigable to the Irwell.