WHITEFIELD — Work began Thursday to remove a roughly 200-year-old dam in the upper Sheepscot River to improve fish passage while providing the town of Whitefield with a more reliable source of water to fight fires. The removal of the Coopers Mills dam – located roughly a dozen miles east of the State House in Augusta – is part of a three-year, roughly $2 million campaign to improve fish passage in a river within the heart of midcoast Maine that is home to Atlantic salmon, sturgeon, alewives and other sea-run fish.