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I knew a guy whose entire commercial diving career was inspecting dams, mostly on the mid-Columbia River. He had some stories. My son was a commercial diver for a few years. He was in-between jobs and took a contract on an earth work dam in Idaho. He was shooting an air lance to look for leaks and found a quite large one. Good thing he didn't get too close. I felt a lot better when he found another line of work.Dams can be quite treacherous.