Lough Ree, the middle of the three great Shannon lakes, stretches north from Athlone for about 25 km, with a shoreline of islands, reedy bays, and limestone karst. The town is the main base for Shannon navigation in this section — boats can be hired by the day or week, and a week on the water exploring the islands and quiet inlets of Lough Ree is one of the great underrated Irish holiday experiences.
The lake is also a serious birdwatching destination. Whooper swans winter here in large numbers, and the islands support one of the most significant colonies of common terns in Ireland. Coarse fishing — mainly bream, perch, and pike — is the other draw. The town's marina is a five-minute walk from the castle.