Complex sentence: The Millpond Dam in North Billerica is just one of many blockages that caused the Alewife population to collapse on the Concord River, and additionally, at this point water was diverted north to Lowell and south to Charlestown to run the Middlesex Canal.
Split into simpler sentences: The Millpond Dam in North Billerica is just one of many blockages that caused the alewife population to collapse on the Concord River. At this point, water was diverted north to Lowell and south to Charlestown to run the Middlesex Canal.