Massachusetts has more than 3000 dams. Dams create artificial habitat by impounding water and altering river function. Impoundments trap sediment and create stagnant conditions with warmer water and lower dissolved oxygen than the rest of the river system. Dams also block the movement of fish that need to access different areas of the watershed and different habitats during their life cycle. Most dams in Massachusetts were built in the 1700s and 1800s to power small mills. These dams have outlived their original purpose and are aging. Many dam owners choose to remove their dams in order to reduce their liability and eliminate the long-term cost of inspections and repairs. The Division of Ecological Restoration (DER) helps interested dam owners remove unwanted dams and restore river processes. Since 2005, DER has removed over 40 dams. To learn more about the process DER uses to select projects for assistance, please see “Become a DER Priority Project”.