I'm currently planning on a multi day kayak trip on the Potomac. I want to do a stretch from williamsport,md to just past great falls. I can't figure out how to measure the river on google earth tho. If it's to long then I will have to shorten it. I'm ok with doing a 4-5 day kayak trip. It's only two of us and we just want a good stretch of river to paddle and relax on. We live in southern Maryland so we don't want to drive to to far to get started. If someone could help me figure out the distance between Williamsport and great falls I would appreciate it. Any other info or advice on places to camp or things to watch out for is appreciated.