Rising water from the Chattahoochee River flooded out Atlanta's sewer treatment plant on Tueday, causing a massive dump of raw sewage into the rain-swollen river.

City officials said the river rose some 12 feet outside its banks, when water flooded into the R.M. Clayton plant in northwest Atlanta near Cobb County. The rising river also flooded out sewage pump stations nearby, causing them to fail as well.

Atlanta officials were trying early Tuesday to assess the damage and see how quickly they could restore the plant and other facilities to working order.

The R.M. Clayton plant is the largest in Georgia with capacity to treat 240 million gallons of sewage a day. It's also connected to the city's controversial combined sewage overflow tunnel, which was designed to hold about 177 million gallons of sewage and rainwater.