I don't know if they pollute the water since they tend to wash up on shore. The issue I see is they will bring a whole different ecosystem into being that feeds on them and that will throw the balance off kilter. More flies, more vultures, more things that eat carrion in general and more things that feed on thing that eat carrion.
Yes this needs to be looked at much closer and see what else has changed with nature. IF this is the start of some major changes then we will need to be ready. With a large bear changing its diet while on the top of most food chains this is not looking good for anyone.