Lady's Island Lake (Irish: Loch Tóchair) is a brackish coastal lagoon covering approximately 2.96 km² in the south of County Wexford, Ireland, situated about 4 km north-west of Carnsore Point — the extreme south-east corner of the island of Ireland. It is the largest lagoon in Ireland and one of only two back-barrier seepage lagoons in the country, the other being the nearby Tacumshin Lake.

The lake is separated from the eastern Celtic Sea by a sand and gravel barrier roughly 200 metres wide. Salt water seeps through this barrier while fresh water enters from agricultural land runoff and several small unnamed streams along the north and western shores, resulting in brackish conditions throughout. The barrier is periodically breached mechanically — a practice known locally as "Cutting the Lake" — to manage water levels, which can temporarily alter salinity and water levels within the lagoon.

The northern shore is characterised by reedy and grassy banks, while the southern banks are sandy. At the north end of the lake lies the village of Lady's Island, where a causeway connects the peninsula to the mainland. The peninsula features castle ruins, a leaning stone tower, church ruins, and a graveyard, and serves as a significant Catholic pilgrimage site dedicated to the Blessed Virgin Mary, with pilgrims gathering each August. Parking is available on the peninsula and in Lady's Island village, and public toilets are available in the village.

The lake holds exceptional ecological importance. It is designated both a Special Area of Conservation (SAC, IE0000704) and a Special Protection Area (SPA, IE0004009) under EU Habitats and Birds Directives. The lake supports the largest mixed colony of breeding terns in Ireland, including the Roseate Tern — the rarest breeding seabird in Europe — as well as Sandwich, Common, Arctic, and Little Terns, and large numbers of nesting Black-headed Gulls. Swans are also regularly observed. The lake hosts rare aquatic flora including Foxtail Stonewort and Spiral Tasselweed, and the critically endangered Cottonweed plant survives on the fringing gravel barrier, found nowhere else in Ireland or Britain. Paddlers should be aware of the lake's protected status and the presence of sensitive nesting bird colonies, particularly during the summer breeding season.

The nearest town is Wexford, approximately 19 km away.