San Joaquin

I have been planning a trip down the San Joaquin River. My understanding has always been that navigation of waters below the high water mark is permitted. These people are claiming that the water is being 'diverted' into the flood ways lying on their property. Can someone please advise me if it is legal for me to continue on down the river in this section? If i am contacted by these guys, i want to have a good knowledge of navigation laws to support us! thanks!