Tacumshin Lake is a shallow coastal lagoon situated on the south County Wexford coast, approximately 15–16 kilometres south of Wexford town and roughly halfway between Kilmore Quay and Carnsore Point. The lake covers an area of about 3 square kilometres and sits on the landward side of a wedge-shaped sand and shingle barrier known locally as "the burrow," which separates the lagoon from the open sea. The Irish name, Loch Sáile, translates as "Saltwater Lake," reflecting the saline character of the water. The lagoon was formerly a shallow sea bay that became progressively cut off from the sea through longshore drift, and it is now largely land-locked, with connection to the sea maintained only through drainage pipes set through the gravel and sand bar.

The lake is designated both a Special Protection Area (SPA, IE0004092) and a Special Area of Conservation (SAC, IE0000709) under EU directives, recognising its importance for lagoon habitat, sand dunes, and stony bank habitats. These designations mean paddlers should be aware that the site is subject to conservation regulations, and any activity should be undertaken with care to avoid disturbing protected habitats and wildlife.

The lagoon is one of the most significant ornithological sites in Ireland, supporting an assemblage of over 20,000 wintering waterbirds. Species of particular note include Whooper Swan, Bewick's Swan, Black-tailed Godwit, Wigeon, Gadwall, Pintail, Teal, Shoveler, Tufted Duck, Coot, Golden Plover, Grey Plover, Lapwing, and Little Grebe. The site is also notable for passage waders and vagrant North American and Eurasian waterfowl, particularly in autumn. The waterfowl population remains diverse throughout the year, which is unusual among Irish wetlands.

Road access to the lake is available at five points, including directly at The White Hole. The surrounding landscape is part of what is described as Ireland's Great Barrier Coast, considered one of the finest barrier coastlines in Europe. The barrier itself shows evidence of landward migration over time, and the broader coastal geology includes Rosslare Complex metamorphic rocks and Caledonian granites associated with the nearby Saltee Islands and Carnsore Point.