If you head away from the river, you head toward Hingham harbor and Webb State Park which are protected bays of the Atlantic. Beaches are available at Webb State Park and nearby Grape Island and Slate Island. The river's current and tides can affect rate of return speed.
OR: From 3A follow Green Street (Jug handle turn by Vietnam memorial) to East to street (left at traffic light) to Puritan Rd. Park at the end of Puritan and bring your canoe/kayak through the gate ( reat Esker Park). It's a short carry to the river from there, and you'll be about 1.25 miles up river from the Rte 3A bridge.