Lough Oughter (from the Irish "Loch Uachtar," meaning "The Upper Lake") is a complex network of lakes and waterways in County Cavan, covering more than 8,900 hectares (22,000 acres). The system sits on the River Erne and forms the southern part of the Lough Erne complex. The landscape is defined by flooded drumlins — glacially formed hills now partially submerged — creating a patchwork of small islands, narrow channels, and quiet bays that make it one of the best inland examples of this type of terrain in Ireland. The surrounding Killykeen Forest Park wraps around much of the lake network.

The character of paddling here is defined by calm, sheltered water and a maze of interconnected channels between wooded islands. The primary destination for paddlers is Clough Oughter Castle, a 13th-century round tower ruin sitting on a small crannog (man-made island) in the middle of the lake. The castle is only accessible by water, making kayak or canoe the standard means of reaching it. The Cavan Adventure Centre offers guided 3-hour kayak tours to the castle from approximately €39 per person, and no prior experience is required. Guided boat tours are also available for those who prefer not to paddle. Stand-up paddleboarding is another option on the lake.

One practical access point is the Killykeen car park, from which paddlers can reach the lake network. A route from Town Lake in Killeshandra through Killykeen to Lough Oughter has been noted as a viable paddle. Water levels on the lake were lowered in the late nineteenth century to reduce flooding of surrounding farmland, which has some bearing on the navigable depth in certain areas.

Wildlife on the lake includes whooper swans and great crested grebes, among other species. The flooded drumlin topography supports rich and varied flora and fauna throughout the system.

The Cavan Adventure Centre serves as a base for organized paddling activities and can provide equipment including kayaks and life jackets. Carafin Lodge at Inishmore, Butlersbridge, also operates on the lake and offers boat hire options. The lake is a well-established angling destination, so paddlers should expect to share the water with fishing boats, particularly in calmer conditions.