The area around Errol, north of Berlin [1], affords the opportunity for both flat-water and white-water canoeing. Located on the Androscoggin River, Northern Waters Canoe and Kayak (Rte. 26, off Rte. 16, Errol, 603/482-3817, www.beoutside.com [2]) rents boats to explore the moose- and waterfowl-infested Umbagog National Wildlife Refuge (Rte. 16, 5 miles north of Errol, 603/482-3415, http://lakeumbagog.fws.gov [3]).
It also leads kayak clinics down the New Hampshire stretch of the Androscoggin River (www.avcnet.org/arwc [4]) on a stretch including Class II and III rapids. Northwoods Rafting (308 Milan Rd./Rte. 16, Milan, 603/449-2628, www.northwoodsrafting.com [5]) also leads white-water rafting trips on the Androscoggin.
Links:
[1] http://www.moon.com/destinations/new-england/new-hampshire/white-mountains/the-great-north-woods/berlingorham-area
[2] http://www.beoutside.com
[3] http://lakeumbagog.fws.gov
[4] http://www.avcnet.org/arwc
[5] http://www.northwoodsrafting.com