Maro Reef is a largely submerged coral atoll located in the Northwestern Hawaiian Islands. It was discovered in 1820 by Captain Joseph Allen of the ship Maro, after whose ship the reef was named. The largest coral reef in the Northwestern Hawaiian Islands, it contains 37 species of stony coral.

Located about 850 miles (1,370 km) northwest of Honolulu, Hawaii, Maro Reef contains about 1 acre (4,000 m²) of dry land which itself can be submerged depending on the tides.