Last sentence is saying that many would find the river too overcrowded for their taste, but if the livery says the water is low less people from the rentals and perhaps other will be on the river.
I have Robert Parnes book (from which most of the excepts that Jim has been posting latey have been taken from) and I think it is a well organized and helpful guide to the rivers of the pine barrens. That excerpt is only part of a longer chapter on the Oswego river.
I agree that the last sentance is alkward, and not terribly logical, but I think Lorun is correctly interpreting it's meaning.
Last sentence is saying that many would find the river too overcrowded for their taste, but if the livery says the water is low less people from the rentals and perhaps other will be on the river.