NEW : four evacuated in Mississippi , Mississippi . Corps of Engineers studies spillway scenarios . Nuclear plant in Mississippi could be affected by flooding . A decision on the spillway 's opening could come between Saturday and Tuesday , officials said . millions of gallons of farmland are flooded in 600 states .
NEW : four evacuated in Mississippi , Mississippi . Corps of Engineers studies spillway scenarios . Nuclear plant in Mississippi could be affected by flooding . millions of gallons of farmland are flooded in 600 states .