It is sourced from the Park Pond in Castle Cary and flows towards the southwest.

Here the river channel has been straightened and drains the surrounding wetland as it heads north to Kings Sedge Moor.

The Cary passes through King's Sedgemoor continuing west across the moors south of the Polden Hills.

Much of the water is now diverted into King's Sedgemoor Drain, which continues across the moors to join the estuary of the River Parrett at Dunball.

[3] In 1995 a major pollution incident occurred when lindane and mercury seed dressing were poured down a drain which leads into the river near Somerton.