 Thanks to Lisa Simpson, Lake Springfield is cleaned up from the pollution that once fouled it. But when Homer, who s adopted a pig (Spider-pig) and dumps a silo full of the pig s crap in the lake, the EPA places a large dome over Springfield, and the Simpsons family manage to escape through a sinkhole. The family flees to a better life in Alaska, but when the head of the EPA, Russ Cargill, orders the towns destruction, it s up to Homer to save Springfield!