My Husky/GSD/Wolf, Jasper hated water, and would not go in no matter what. He would stand at the shore and whine/bark if we got in.
Woody couldn't really care less about water, its the Fishies that he wants
Maple was afraid of water until she saw my BIL's lab/rottie fetch a stick in the water, then, something clicked. She went in (ears pinned back--her "work" mode), swam out to the stick, and came right back to shore stickless LOL Now, she'll go in, but, she's always in work mode, not play or enjoyment.
Maybe if Zeus sees other dogs swimming, he'll get the point? Or, he might have been worried since the kids were afraid.