Marine pollution is the release of by-products of human activity that cause harm to natural marine ecosystems. The pollutants may be sewage, farm waste, toxic chemicals, or inert materials that may smother, choke, or strangle living organisms.

Sewage, Animal Waste, and Fertilizers

Sewage, animal waste, and chemical fertilizers all have a high content of nitrogen and phosphorus. Artificially high levels of these substances in the water promote excessive growth of microscopic or macroscopic plants, in a process called eutrophication. When these plants accumulate, die, and decay, they cause low oxygen content in the water. Even if sewage is treated to remove solids, the liquid discharged contains high levels of nitrogen and phosphorus. Intensive cultivation of animals in feedlots, or application of more fertilizer than a crop can absorb, also cause runoff rich in nitrogen and phosphorus that find their way into rivers and estuaries...