Emergency workers are prowling streets outside Boston in boats, warning people to get out of their homes before they're trapped by floods.
Heavy, constant rain has flooded the Merrimack River. Forecasters predict it will keep rising.
Widespread flooding north of Boston, near the New Hampshire line, has sent hundreds of people from their homes.
Tens of millions of gallons of sewage is spilling into the Merrimack after pipes burst in Haverhill Sunday and a treatment plant in Lawrence was knocked out Monday.
New Hampshire's governor says more than 600 roads are damaged, destroyed or under water.