Oil spills, like the big spill from the oil tanker Exxon Valdez in Alaska in 1989, kill large numbers of animals. Many smaller spills and leaks go relatively undetected, but their cumulative effects over the years also can injure wildlife. Water is not the only element that suffers from pollution. Factories and cars release chemicals into the air. The chemicals are deposited on land by rain, causing pollution, including what is known as acid rain.
Acid rain weakens and kills plant life, decreasing the food supply for animals that eat the plants.
Pesticides are another source of pollution. Farmers use pesticides to keep insects from eating crops. Insects also carry pesticides. The chemicals can disrupt physical functions like reproduction in these animals. We know less about other factors that probably contribute to the decline of biological diversity.