The River Lagan 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 natural feature, providing habitats for various wildlife and recreational opportunities for residents and visitors. The Lagan is known for its scenic beauty and is lined with walking and cycling paths. It plays a significant role in the history and development of Belfast, serving as a vital waterway for trade and transportation in the region.