More than likely this time of year they are catfishing. I fish below the dam regularly and going under the dam is not as bad as you'd think. I've done it more times than I can count fishing and catching bait. I wouldn't recommend it with someone inexperienced, or in a fiberglass boat. Those concrete walls under there along with the current will do a number on fiberglass. Also, if the turbines are completely off, stay away. If you're under there and the turbines are slowly runnning and they increase them it's no big deal. If they're completely off and they turn them on while you're under there....you'd better hold on....it's gonna get rough!