The River Lagan is a major waterway in Northern Ireland, running approximately 54 miles from the mountains of County Down through Belfast and into the Irish Sea. For paddling purposes, the river is divided into two distinct sections by a weir at Stranmillis, each suited to different experience levels.

The upper section runs between Drum Bridge and Stranmillis Weir and lies at the heart of Lagan Valley Regional Park, which extends 11 miles along both sides of the river between Stranmillis and Union Locks in Lisburn, covering around 4,200 acres. This stretch contains several weirs and is considered more suitable for experienced paddlers. Downstream of Drum Bridge there are three weirs to cross before reaching Edenderry, followed by a relatively flat section from Edenderry to Shaws Bridge. Below Shaws Bridge there is a weir and slalom course. Access on this section is available at Minnowburn and Shaws Bridge.

The lower section, between Stranmillis Weir and Lagan Weir, covers approximately 3 miles (4.8 km) and is largely flat water, flowing through Stranmillis, Annadale, Ormeau, and Ravenhill into the city centre. Paddlers are required to keep to the right-hand side of the river and always pass on the right. There is no water access at Annadale. Access points on this section include Governor's Bridge at Stranmillis (pontoon, managed by the Department for Communities), Ravenhill Reach on Ormeau Embankment (public slipway and pontoon, also managed by the Department for Communities), Maysfield Basin at May's Meadow (steps, managed by Allstate on behalf of Belfast City Council), and Lanyon Quay at the rear of the Waterfront Hall (pontoon, managed by the Department for Communities). Access to managed pontoons requires contacting the River Manager at 028 9031 5304.

Speed boats, jet skis, and water skiers are not permitted on the river except during approved events. The river is also actively used by rowing clubs, particularly near Belfast, and a commercial river boat operates from the weir offering tours. The Lagan Watersports Centre provides sailing and canoeing on the river, and kayak and paddle sports rental facilities are available within Lagan Valley Regional Park. The Department for Communities publishes a Guide to the Tidal Lagan covering navigation through Belfast city centre.