University of Massachusetts at Lowell
Races of various lengths are held on the merrimack River, finishing near the UMass-Lowell boathouse.
Map and directions: 381 Pawtucket Blvd, Lowell, MA 01854 is the main parking area.
There are a few other parking options, and some important notes on what not to do, at the Textile River Regatta website: click [Parking]. One of the best resources on the site is the area map, reproduced below; note that it's oriented with North to the right. There is also a course map at the TRR site.