There are three main types of coral reefs: barrier reefs which are separated from shore by channels, fringe reefs which grow closer to shore than other reefs, and atolls which surround a lagoon. Coral reefs are found in shallow, unpolluted waters near the equator in areas like Australia, the Indian Ocean, and Pacific Ocean as they need certain temperatures to survive. However, coral reefs are increasingly threatened by human activities such as taking coral for aquariums, boat damage, and pollution.