It is on the Duddon Estuary near the town of Millom and covers an area of 3.28 hectares (8.1 acres).

The reserve continues to be protected from the sea by a seawall built by John Aird & Co. and completed in 1905.

The lagoon was originally a separate Site of Special Scientific Interest (SSSI), notified in 1983.

In the case of Hodbarrow, slag was moved to create a new island in the lagoon for the benefit of little, common and sandwich terns.

[8] Hodbarrow is also renowned for large numbers of wildfowl during the winter, especially teal, wigeon, coot, mallard, tufted duck, common pochard, goldeneye, red-breasted merganser, and occasionally long-tailed duck, eider, goosander, pintail and shoveler.