Ruth Island (also known as Ruth Cay) is an artificial island off the south coast of Saint Croix, U.S. Virgin Islands near Port Alucroix. It was created in the mid-1960s from the dredging of Krauses Lagune and is about 40 acres (0.16 km²).
Because the island is free of small Indian mongooses (Herpestes auropunctatus) biologists introduced the endangered St. Croix Ground Lizard (Ameiva polops) from the Protestant Cay population. Today there are about 30 ground lizards on Ruth Island.
Coordinates: 17°41′1″N 64°45′43″W / 17.68361°N 64.76194°W / 17.68361; -64.76194