Good point! It's all the more frustrating because there are so many lakes and streams in the parks, but have you ever tried to fill up a water balloon from a lake? It's easier to just by chicken nuggets to toss at them.
Back on the topic of the best lens, I spent some time at Epcot last night using only an 85mm prime that I just got. Posted a photo of Alice in the Portrait thread.
Lovely lens for low light and great bokeh, but 85mm is a bit long for most shots that I'd take. When I tried to switch to detail shots, I found that it has a longer minimum focus distance than I could use to get in close enough to fill the frame.