You can launch from Seabrook location, right after the bridge on the right side...there are toilets too.
Odiorne (from nspn.org) : Seavey Creek/Odiorne
A popular put-in in the Portsmouth area (Rye, NH) is Seavey Creek, just before Odiorne State Park. From the North or West, head S on Rte 1 at the traffic circle. Travel 2.0 miles(you will cross Sagamore Creek), and turn left onto Elwyn Road at the traffic light. Travel 1.4 miles to Foyes Corner, and proceed straight on Rte. 1A (Pioneer Rd) for 1.1 miles to Seavey Creek. There is free, sometimes congested parking on the near side of the Creek, and the launch is muddy. A $5 parking/launch fee is charged at the lot on the far side of the Creek, but there is a gradual cement launching surface.