Joppa Flats is located in the mouth of the Merrimack River. The fishing is incredible at times. You have to launch and be off the water within 3 hours +/- high tide or you will be dragging your kayak through the mud. Currents and winds can change rapidly as well as fog can appear out of no where so be prepared. Also you want to stay away from the channel that leads out to open ocean, the currents can be treacherous.