For 10 points, name this largest river of Boston.
This river is home to the Hemlock Gorge and Elm Bank Reservations. The Hatch Shell lies on this river's namesake Esplanade and its current river basin was created by James Storrow. One of this river's tributaries flows from Jamaica Pond through Olmstead Park and drains into the (*) Fens in addition to draining into this river, while another of this river's tributaries originates at Turtle Pond in a namesake reservation and once drained into the  ► Back Bay. Those waterways, the Muddy River and Stony Brook, are tributaries of this river which runs past the Watertown Dam and Waltham. For 10 points, name this largest river of Boston.
This river is home to the Hemlock Gorge and Elm Bank Reservations.
Charles River