;Annie,
My sister-in-law lives on Long Island, NY and has had a Koi pond for a number of years. In the beginning, she began to notice that her fish were disappearing. Finally, she caught the culprits in the Act! OSPREYS were swooping in and stealing her fish! She had put up a thin string netting over the pond to keep them out.
I had once thought about putting a pond in when we first moved into our house, but I had a friend/neighbor tell me she took her pond OUT because the local bears were eating her fish! 😲
Jane