The River Mersey starts in the Portwood area of Stockport, Greater Manchester, where the River Tame and River Goyt meet.
The River Goyt originates some 14 miles (or 22.5 kilometres) to the southeast on Axe Edge Moor in the Peak District, and the River Tame starts 14.5 miles (or 23.3 kilometres) to the northeast at the Readycon Dean Reservoir on Denshaw Moor.
From its headwaters at Stockport, the River Mersey continues westwards and ultimately flows into the Irish Sea near Liverpool.