The Mousam River is a tidal river, which means the current changes depending on the tides. Between Low and High tide, the river flows "backwards" from the Ocean northward, and between High and Low tide, it flows southward toward the Ocean. The ideal time to paddle up river, is around high tide. To plan your trip, try to have high tide aligned to be half way through the duration of the trip. For example, if you're going on a 3 hour paddle, leave 1 1/2 hours before high tide.
The easiest launch site is at the Route 9 bridge (approximate address is 210 Western Avenue, Kennebunk, Maine) with plenty of free parking along the road. There is also a launch site at Rogers Pond Park, also with free parking (entrance near the corner of Water Street and Factory Pasture Rd, Kennebunk, Maine), which is at the northern end of the navigable part of the river. This is also a great place to stop for a break when paddling up river from the Route 9 bridge.
The river flows into the Ocean at Parsons Beach, which lies to the west of the mouth. The entire navigable length of the river is 3 miles, with the route 9 bridge being 1/2 mile from the mouth, and the Railroad bridge being 2 1/2 miles from the mouth.
The Mousam River is a great place for a quiet paddle, with very little boat traffic, and plenty of wildlife, especially Birds (including Bald Eagles, Hawks, Egret, Herons, and many more.