Pond Boss Forums GENERAL QUESTIONS Wildlife Management Birding

So I look out at the pond today and see 3 black birds in the hole from the aerator. Don't have my new binocs yet so I think cormorants. Throw on the boots and a coat and head down to run them off. When I get there, number 4 pops up from dive. About the size of a good size duck, black backs and head with white breast and body. They flew away with the rapid wing movements of a duck. I did not have a camera and I dun see that well anymore so that's all you get for a description. Any thoughts on what they were?

Edit: I have ruled out penquins