HAVING to? low.
why fly in? the road to Boundary creek is usually clear by the beginning of the month. Otherwise you can float Marsh Creek. The obvious risk is high water depending on your launch dates, but are you going to want to fly in regardless if the water is too raging for your likes? You will cancel not for the difficulty but more for the risk.
It think most people think of flying in instead in August because they don't want to handle the low water in the upper section.
Hey, if you want me to take a dump in a box and mark it "guaranteed", I will. I got spare time.