Just got back from the beach. Spoke to the Head Lifeguard. He agrees that all but one of the pictures does not need a release because the person is not recognizable. The one pic of the girl guard standing on the ramp of the guard platform (the second pic) is a "maybe" so we'll ask her for a release just for good measure.
I gave a 4x6 to everybody I took pictures of and told them what I was planning. They were all happy to have a picture of themselves and thought it was a great idea.
I left the release at the guard shack and it'll get passed on to the person in the picture at the end of the day's shift. I can pick it up tomorrow.