Dioxin in fish tissue is the most significant problem in major rivers. Oxygen-depleting substances from nonpoint sources and bacteria from inadequate sewage treatment are the most significant problem in smaller rivers and streams. Lakes are impacted by oxygen-depleting substances and mercury from atmospheric deposition and nonpoint sources, including urban runoff, agriculture, and forestry activities. Bacteria from municipal treatment plants and small dischargers contaminate shellfish beds in estuarine waters. The most significant ground water impacts include petroleum compounds from leaking underground and aboveground storage tanks, other organic chemicals from leaking storage facilities or disposal practices, and bacteria from surface disposal systems or other sources.
Maine requires that all underground tanks be registered and that inadequate tanks be removed.
About 23,000 tanks have been removed since 1986. Maine also regulates installation of underground storage tanks and closure of landfills to protect ground water resources from future leaks. As the State makes progress in restoring waters impacted by point sources, new water quality problems emerge from nonpoint sources. Therefore, the most important water quality initiatives for the future include implementing pollution prevention, nonpoint source management, watershed-based planning, coordinated land usemanagement, and water quality monitoring. The State is linking pollution prevention with the watershed protection approach in a pilot project within the Androscoggin River basin.