Ōike (大池) is a karst pond on Minamidaitōjima, Okinawa Prefecture, Japan. Ōike is the largest pond containing both freshwater and seawater. It covers 0.31 square kilometres (0.12 sq mi), the circumference is 5.50 kilometres (3.42 mi), and it is 1.3 metres (4 ft 3 in) at its deepest point. Fresh water is mixed with seawater beneath.