The Saco River has several swimming holes for a quick dip. Check out the small beach at Davis Park (Eastside Rd., Conway), scenically situated just beneath a covered bridge.
North Conway has its own Echo Lake in Echo Lake State Park (off Rtes. 16/302, 603/356-2672, www.nhstateparks.com/echo.html [1], $4 adults, $2 children 6–11, free children under 6), which offers a beach, trails, and picnic area with a view of Cathedral Ledge above.
The Saco River might not be the fastest river in New England, but it’s certainly the most popular due to its wide, gentle current and well-developed infrastructure of campgrounds. Saco Bound Outdoors (Rte. 302, Center Conway, 603/447-2177, www.sacobound.com [2]) is the local expert in guided trips down the river; it also has canoe rentals and shuttle service for trips of any length.
Links:
[1] http://www.nhstateparks.com/echo.html
[2] http://www.sacobound.com