The Presumpscot River is the largest freshwater source to Casco Bay.  It flows for 26 miles from Sebago Lake to Casco Bay, through one of the most developed and fastest growing watersheds in Maine.  Since 1989, Presumpscot River Watch (PRW) has been helping to preserve and improve the health of the Presumpscot River and its watershed.  Volunteer-driven, the group conducts scientific monitoring and shares data to increase public awareness.  In addition, PRW serves as steward for the river through participating in legislative, community, and individual efforts.

Water quality monitoring volunteers sample the river twice a month from May through August, measuring dissolved oxygen, temperature, and levels of Escherichia coli (bacteria) at 30 sampling stations distributed along the mainstem and tributaries of the river.  Citizen volunteers are also trained to assist with laboratory analysis of water samples, following a Maine DEP-approved Quality Assurance Project Plan.  CBEP supports the PRW monitoring program by providing annual funding.