Pollution comes in many forms, but all of them impact the marine environment. Runoff, harmful contaminants such as fertilizers, detergents, sewage, plastics, and other manmade pollutants reach the ocean, often starting far inland. When these enter the ocean, the fish are subjected to them and the pollutants enter the food chain. Still other pollutants end up directly killing sea life; pollutants such as plastic trash and bags.
Noise pollution, believe it or not, impacts the oceans since sound waves can travel for miles. Sonar, sounds from ships, oil rigs and other noises disrupt the migration and living patterns of most marine animals, especially those that use echolocation and sonar, themselves (dolphins and whales).
Oil spills. Single most impacting event to the ocean. It's effects are long lasting and devastating to everything on a macro and micro level.