That mowing angle can be a tricky one. I thought mine was pretty shallow above the waterline and even drove over it with my small tractor to make sure it wasn't too steep. Then as the grass started to grow and the rains eroded part of it and the water level rose, my plan went right out the window. I can mow all around my pond, but there are places that I'm out of the seat as it's so steep and bouncy due to the ruts. Walking around it, the ruts look small. In fact, with the grass grown in, you can't see the ruts. But on the tractor mowing, you sure can feel them.
There is only so close to the water that I can get before sinking in. I cannot mow to the waters edge, it's just too soft for the weight of the tractor. What are you going to mow with and how close to the water do you want to mow? If I was to do it again, I would make my slope allot less. I still might with the dozer if the rains stop long enough and the water drops down to where I don't have to worry about getting stuck.
My neigbhor is digging a pond and his dam is done. He's still digging out the pond itself with a pipe through it for a drain. It might take him a few more years to get it dug this way, but he's trying to maintain his dam. His slope is too much for his tractor and he's doing it by hand with a weedeater. He might have to add a massive amount of dirt to get a slope that he can mow, but until then, he's struggling to keep it under control.
Eddie