The biggest problem with national parks are that humans are too careless.  We pollute the parks which cause even greater problems.  Rivers, lakes, the land, and the air gets polluted and animals pay the price.  Eventually, a lot of animals are going to become endangered and we are going to wonder why, when in reality, it was our fault all along.  We all need to realize the damages we put on our parks and fix them or we won't have them anymore.