Diablo does maintain a jolly 50F water temperature all summer long. Ross tops out in the lower 60's.. We got surprised by 30mph winds on Diablo that came up with no warning - steep 2-1/2 ft waves, it was a struggle to get to shore right side up. The NPS campground registration system for Ross takes no account of the fact that you might get windbound. As pretty as it is, it was one of the most bullsh*t canoeing experiences I've ever had, and not because of the weather. There's better places to paddle than that.