The Lagan River is a river in Northern Ireland that flows through the city of Belfast. It stretches approximately 40 miles (64 kilometers) from its source in the Slieve Croob mountains to its mouth at Belfast Lough. The river is an important waterway for the region, historically serving as a trade route and a source of water. The Lagan River is also known for its scenic beauty, with walking and cycling paths along its banks. It features several bridges, including the iconic Lagan Weir, which helps manage the river's flow and provides a picturesque view for visitors and locals alike.