Small bits of plastic and wire kill many sea creatures.
Many animals may get tangled in fishing line.
When humans swim in polluted water we swallow that water which may cause serious illnesses like cholera, typhoid fever and gastro-enteritis. These diseases are often fatal.
Bigger animals eats smaller animals. The littlest organisms can become poisoned by polluted water. They intern are eaten by other animals. The result is that even whales eventually suffer.
Even humans form part of the poisoned food chain.