The River Blyth flows eastwards through southern Northumberland into the North Sea at the town of Blyth. It flows through Plessey Woods Country Park. The River Pont is a tributary. The Blyth is long and the Pont is .
The tidal limit of the river is at Bebside. The estuary widens from this point eastwards and with the addition of a burn that enters on the northern side (Sleek Burn), it covers an area of .
Ecologists have suggested that a dam on the river at Humford Country Park in Bedlington could be removed to allow for fish migration. The local community have expressed a desire to keep the dam as it is a local beauty spot; they have suggested that a fish passage be built alongside instead.