if they happened to sprout and actually grow into a plant wich isnt likely without an occasional visit but if a few plants did grow then yes the buds would be smokable but full of seeds and probably wont be to enjoyable picking out all those seeds but it can still be potent.
even if you just visited every couple of weeks to weed them and get them established and sexed you would be alot better off, but if its on a river bank flooding should be a big concern theres not many spots on river banks that dont overflow its banks after alot of rain