Camo is great and absolutely necessary for some pursuits, like ducks and turkeys. Despite what Cabela's would like you to believe, it is helpful for deer but not necessary. If the wind was right and he wasn't moving, I bet those deer would have walked right past Marvin even if he was wearing cut offs and a Vols jersey. Scent and movement is primarily what is going to bust you in the deer woods- though I have had deer see me a few times when I wasn't moving and the wind was good.
Along a trout stream, the thing that will do you in first and foremost is sound produced in the water (often through the bank). And after that shapes and movement. This includes shadows cast on the water, heads sticking over banks, the ends of fly rods false casting over a long pool, etc.
I often wear camo fishing but that's because half of my closet is camo clothing. And by closet I mean the big pile of clothes on the floor. I always wear subdued tones. I walk soflty along the bank. I try to stay low and downstream when I must approach close, and I alway keep something to my back. I am constantly suprised at how much I can get away with if I have a bush, a tree, or a boulder behind me, hiding my movement and silhouette.
As far as what people in the park think: How will they see you if you are cammied up? (little smiley face to show that I am ending on a humourous note)
Life is hard. But it's a lot harder if you're stupid.