A lagoon is shallow waters near land, which is separated from the ocean by either a coral reef or a piece of land exposed out of the water. A lagoon may consist of parts of reefs, meadows of marine macro plants, coral debris and sand. A small and shallow lagoon, with small ripples can have very hot water, as it is constantly exposed to the sun and a small wave effect. Others, near forests of mangrove plants or areas affected by human activities, usually have very turbid waters and high concentrations of nutrients. Thus, it is difficult for corals to live in lagoons.