 The River Parrett originates at Cheddington , Dorset , just over the border with Somerset . It enters Somerset at Haselbury Plucknett where it is joined by the Broad river . It passes to the east of South Petherton and flows north through Thorney Moor and Muchelney Level and it is then joined by the Isle and Yeo ( Ivel ) rivers . The Parrett flows through Langport and then through Middle Moor , Aller Moor to Burrowbridge where it is joined by the River Tone . It then passes through Earlake Moor , Hartlake Moor , Weston Level and South Moor . It continues north through Bridgwater , Horsey Level , past Pawlett Ham and Pawlett Level to the coast near Burnham @-@ on @-@ Sea . 
