Evolution Creek stream crossing "should be" do-able by mid-August; it's one of the deeper crossings. When approaching the crossing on the trail, don't go straight across (sometimes waist deep), but go upstream about 100 yards to the shallow section and cross there.
When we did the JMT in 2006, we were able to do straightforward crossings everywhere at the end of July. I remember Bear Creek and Evolution Creek as the diciest. I assume that this is going to be a heavy flow year. I would definitely try to get as much advice as possible on crossings. By August, there should be plenty of reports available.
