The Kennebunk 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 river flows into the Ocean at Goochs Beach, which lies to the west of the mouth. The entire navigable length of the river is 5 miles, with a 1 mile stretch from the mouth of the river to the Dock Square bridge not recommended for kayaking due to boat traffic. If you must travel on this lower stretch, please make sure to stay as far as possible to the right side of the river, in order to give boats plenty of room. Make sure you stay well aware of your surroundings, and check all around you for boat traffic. Above the Dock Square bridge, the river is closed to navigation, and you may paddle in any part of the river. Durrells Bridge is 3.3 miles, and the Railroad bridge 5 miles from the mouth. The river becomes unnavigable north of the Railroad bridge.
The upper section of the Kennebunk River (above the Dock Square bridge) is a great place for a paddle, with very little boat traffic. The only public launch site north of Dock Square, is at the old Grist Mill, a property owned and maintained by the Kennebunkport Conservation Trust. It is located at the end of Mill Lane in Kennebunkport, just north of Dock Square. Please note that parking is not allowed at this location, so after you unload your kayak you must find parking at the municipal lot or on one of the streets which allows parking.