Compensating for Current?

Hi folks, I am planning a swim for later in July, in the Western Massachusetts area, on the Connecticut River. Basically, in case any of you know the area, I want to swim the approximately 15 1/2 miles from the Sunderland Bridge to Northampton. My question relates to determining how much assistance the river is giving me current-wise. I know that will depend upon the height of the river, etc., but is there a general way to determine things like that? The idea is to do this as a "practice" swim for a later event, in September, to be open to others. This time, however, it will be just my husband in the kayak and me in the water. Thanks for the help! Sydne