all right. welcome back. now a story about the nation's all right. welcome back. now a story about the nation's lakes being invaded by a slimy enemy. there's nothing nice about this stuff. it is smelly, and it looks bad. >> all that and it's dangerous. abc's jim avila went to wisconsin, put on some waders, and got into the story literally. >> reporter: it's an assault on nearly all the senses. a living, breathing, growing, toxic organism known as blue/green algae, and it is worse this month. >> that is very much alive. >> reporter: gosh, the smell is bad. caking america's lakes so thick, the swirling slime can be seen in photos from space. >> people that used to be here, after a couple of years said we can't handle it anymore and left. >> reporter: tom runs the marina in lake petenwell, wisconsin, or tries to. >> nobody will swim or boat in it.