Experts say farm chemicals are the big source of Mississippi River pollution. But farmers point the finger right back at urban areas and say city dwellers need to do more to clean up their act. Tens of millions of dollars are being spent to upgrade the Twin Cities sewage treatment system to do just that. The goal is to remove phosphorous from sewage. Environmentalists applaud the action as a step in the right direction. But they say the Mississippi's health will improve only when more far reaching steps are taken to restore the river's ecology.