Complex sentence: Several boathouses were built along the "Lakes District" of the Charles, stretching several miles from a dam in Waltham and as many as 5,000 canoes would crowd the waters on weekend days in the summer.
Split into simpler sentences: Several boathouses were built along the "Lakes District" of the Charles, stretching several miles from a dam in Waltham. As many as 5,000 canoes would crowd the waters on weekend days in the summer.