Ferry routes are often indicated as they function as a road of sorts. Without bridges or sufficient bridges for the flow of traffic it would be certain to have ferries. It would also have shipping without a doubt. Shipping channels are not likely to be indicated in anything but a nautical map, and even then all they indicate is the safe part of the river in terms of bottom clearance. There would also be dredgers, water taxis, fishermen, people living on boats etc. Think Hong Kong. I say this because it seems to me that the river would be the center of their life and civilization given he otherwise remote appearance of your location. They would directly rely on it and also on cities farther down the river.