Surface water

The Blackstone River basin drains about 335 mi2 of south-central Massachusetts. About 67 percent of the basin is forested, and about 3 percent contains lakes. Many of the basin's lakes and ponds were created or enlarged by earthen dams. In total, there are 183 lakes and ponds, 107 of which have an area of at least 10 acres. The largest lake is Lake Quinsigamond in Shrewsbury and Worcester, which is 781 acres.

The Blackstone River begins in the southern part of Worcester at the confluence of Middle River and Weasel Brook and flows southwestward about 31 mi through a narrow valley before crossing into Rhode Island. The gradient of the river is moderate, averaging about 11.5 ft/mi from the headwaters area near Worcester to the USGS streamflow-gaging station at Woonsocket, R.I., a distance of about 43 river mi. Tributary streams draining the western uplands tend to have steeper gradients than those draining the eastern uplands. Although Worcester is supplied with water from reservoirs, public supplies for most other communities in the basin are obtained from ground water.