Businesses and cities dump sewage, garbage, chemicals, nuclear waste and more into the oceans, perhaps thinking that it will go away. But it is destroying oceans and the creatures living in them. The city of Vancouver alone dumps over 756 million litres of sewage into the ocean every day. If the waste doesn't affect the whales right away, it may get to them when they eat smaller fish and organisms which carry toxins in them. Fish nets are another hazard that may trap whales, holding them under the surface so that they can't breathe.
Noise pollution is another problem - whales use sound primarily to observe their world.
Gray whales may be quite effected by the continual sound of the heavy boat traffic that exists on their migratory routes.