Coral reefs need clean water in order to survive. Pollution like untreated sewage, run off and wastewater can cause major damage to coral reefs. In the Carribean, around 85% of the wastewater that enters the ocean is untreated. Places that are more heavily populated can have a larger affect on the situation, due to more runoff and pollution. It just so happens that the heavily populated areas are also the place where most coral reefs are located. [3]
Land-Based
Human activites, like deforestation and land-clearing, can lead to erosion flowing down the rivers and polluting the ocean water. On farmlands, pesticides, livestock waste, and fertilizer contaminate the rain water that flows into the ocean. Solid waste from landfills and dumps may also end up in the ocean. The sediments, toxins and nutrients coming from these wastes can stress and kill the coral. With more precipitation, comes more erosion and runoff polluting the water. [4]
Sewage
There is a mixture of things in sewage that ca be very harmful to coral reefs. The main factor in sewage is fresh water, which is actually stressful for coral. Many unknown chemicals are in sewage which are unhealthy for not only coral reefs, but humans too. Metals such as lead, copper and mercury can be found in sewage which can increase the amount of pathogens on coral reefs and can cause infection . Pathogens such as viruses and bacteria are a major cause for illness in people and in coral. Toxins like pharmecuticals and antibiotics also end up in sewage, causing problems for the coral. [3]
Marine-Based
Vessels that reside in the water distributes a large amount of pollution. Commercial, passenger and recreational vessels contaminate the water with fuel, sewage, solid waste, and more. Many vessels leave behind debris like fishing gear and oil that harm the coral and species living in the water. There have been many occurrences where fishing nets that have been left behind became entangled with turtles and fish. The oil can stress the coral by killing the tissues, zooxanthellae will leave, etc. [4]