Rakahanga is just over 4 square kilometres in size. Its highest point is about 5 metres (17 feet) and like the other Northern Group atolls, Rakahanga is in danger from rising sea levels. Its large lagoon is shallow with poor sea water circulation, which is unfavourable for coral growth. The natural entrances to the lagoon are narrow and shallow, passable only by canoes and small boats with skilled captains. A deeper channel was created in about 2015 under a Harbour Improvement program.