I used to mow around my pond with my JD 5300 until my neighbor went over sidways to end up upside down in 10 feet of pond water while mowing on his Kabota. It was a typical tractor accident in that he was underwater before he knew what was happening. Fortunately, he was buckled in and saved by his ROPS from being the bug on the windshield. He was able to unbuckle and swim out. He and I both use lawn tractors for mowing near our ponds now. As long as you mow side to side, sit on the high side, and don't play around at the waterline, it is safe.
Lou