I've seen the Mink on the banks of the lake but never in it, where it shouldn't really have any chance of catching anything. I suspect the Mallards were swimming very close to the far shore when the Mink decided to launch itself at one of the youngsters.
Unfortunately the far side of the lake is out of the reach of my 500mm lens, even with the 1.4x converter attached. But you can just about make out the head and shoulders of the Mink as he swims after the ducks.
Some of the family decided to take refuge on an abandoned Coot's nest.