When I saw the eagle swimming I thought it had killed a duck or other seabird. It is fairly common for eagles to swim , towing their kill, if it is too heavy to fly with. This one was making better speed than they do when pulling a heavy fish, which I've seen more often.
When he (or she ) got to shore he rested for several minutes. Then he pecked at the meal just a bit and followed that with a distinctive eagle cry. He must have intended to share.
After the gang had dispersed I went over with the boat and found the head and neck of a Blue Heron. I think the eagle must have attacked this big bird while it was in flight over the bay.