Just 20 years ago, the Penobscot River near Bangor was packed with anglers who came from across the country to catch a fish in one of the prized salmon pools. But dwindling numbers of salmon caused them to be declared endangered in 2009, ending salmon fishing on Maine’s largest river. Environmentalists say the removal of the Veazie Dam could be a monumental step toward restoring the salmon population and resurrecting a rich history of angling on the Penobscot River. It will start to come down Monday. The hydropower dam’s removal will allow salmon to avoid its deadly turbines and pass freely to more spawning habitat. The destruction of the Veazie Dam is part of the Penobscot River Restoration Project, which also included the removal of the Great Works Dam upriver last summer.