We were kayaking the other day and a couple of teenage girls had tipped over in their boat. When they got back to the dock, the workers told them not to play in the water, that it will hurt your skin.
I guess that's one way to discourage people from swimming in it. But we also watched last weekend as some people were swimming in the lake, and the security guard was on his bike under the bridge just sitting there watching. We waited to see if he went to kick them out, but never did. I wish I had a local badge, I'd take charge and get the non residents out of our lake