The River Tweed is 156 km long and flows primarily through the Borders region of Scotland and England. It rises on Tweedsmuir. At Berwick-upon-Tweed, it flows into the North Sea. It drains the entire Borders region. Its lower reaches mark the Scottish border with England for 27 kilometres near Berwick-upon-Tweed. The Tweed is one of the great salmon rivers of Great Britain.