natural: volcanoes,algae blooms, animal waste, silt from storms and floods (runoff)
human: sewage, pesticides, fertilizers, waste water, chemicals from factories, silt from construction, trash from littering
oil spills: Exxon Valdez oil spill “caused by an oil tanker hitting a reef off the coast of Alaska- over 11 million gallons of oil spilled into the ocean.”
acid rain: sulfur dioxide gets high into the air they combine with rain and produce acid rain because of evaporation