Other idea for dystopian novel

My initial idea for my dystopian novel was not a very good one in my opinion, so I have a new idea. There has been a scare around for a long time that if the bottom of the food chain were to become extinct the other animals would also die. This is what gave me the idea for my story: the seas have become so polluted that fish can no longer survive, this leads to other animals dying. The human race has become extremely unhealthy, and selective breeding has come into place, so people who are unhealthy are discriminated, so that they will end up dying. But this means a lot of cross breeding ends up taking place…