Answer:
Most ocean pollution begins on land
When large tracts of land are plowed, the exposed soil can erode during rainstorms. Much of this runoff flows to the sea, carrying with it agricultural fertilizers and pesticides. ... One of the biggest sources is called nonpoint source pollution, which occurs as a result of runoff.
The lack of care on surface water affects all oceans, rivers, and lakes directly, where pollution like agricultural chemicals affect ground water, which eventually makes it to the sea. Causes of pollution include oil (35% from city runoff), agriculture pesticides and fertilizer runoff, garbage misplacement, and mining.