Shagnasty Island is a small, rocky ice-free island lying 0.3 miles (0.5 km) west of Lenton Point in the north part of Clowes Bay, close off the south coast of Signy Island in the South Orkney Islands. Roughly charted in 1933 by Discovery Investigations personnel, and surveyed in 1947 by the Falkland Islands Dependencies Survey (FIDS).