The River Lagan (from the Irish: An Lag�in meaning "river of the low-lying district") is a major river in Northern Ireland which runs 40 miles (60 km) from the Slieve Croob mountain in County Down to Belfast where it enters Belfast Lough, an inlet of the Irish Sea. The River Lagan forms the border between County Antrim and County Down. The Lagan Towpath is a pathway which runs from Lisburn to almost the centre of Belfast.