I had three sets of ducks. A pair of Mallards, a pair of Black Swedish, and a pair of Cayugas. The Mallard hen went missing during the winter and everything was OK. Opened their 300 gal. pool in early March and Cayuga female went missing. Found her at the bottom of the pool. Watched all three drakes almost drown the Black Swedish hen. Once one mounted her, they all took turns until she almost drowned. I yelled at them from the deck and she was finally able to crawl out of the water with her wings (like a teradactyl). We've since drained the pool and sequestered the female. It's not fair to keep her from her flock, but they are going to kill her. What do we do?