Surface water

The Deerfield River flows southward from its headwaters in south-central Vermont and joins the Connecticut River at Greenfield, Mass. A little over one half of its 664-square-mi drainage area, 347 mi2, is in Massachusetts. The river flows southeastward through the Berkshire Hills of Massachusetts in a narrow valley bordered by steep slopes that rise, in places, more than 1,000 ft above the river. Near the Connecticut River, the terrain is much flatter. Overall, the gradient of the Deerfield River is quite steep, averaging 46.8 ft/mi from its headwaters to the USGS streamflow gage near West Deerfield, a distance of about 69.5 river mi. The basin contains relatively few lakes and ponds, and most of these were created or enlarged by earthen dams. There are a total of 23 lakes and ponds, 16 of which cover at least 10 acres. The largest lake is Sherman Reservoir in Rowe, which has an area of 162 acres.

The natural flow of the Deerfield River has been modified by the reservoirs in Vermont. More than 200 Mgal/d of water are withdrawn from the Sherman Reservoir in Massachusetts and Vermont to cool the nuclear-fuelled power plant at Rowe, Mass. The cooling water is returned to the reservoir and used downstream at hydroelectric power plants. Water released from the reservoirs during periods of power generation causes diurnal fluctuations in streamflow. The reservoirs help control floods in the basin and augment flow in the Deerfield River during low-flow periods.