An old boss witched a well many years ago and the well they bored provided water for a 20 acre market garden. He used a forked stick. His mate seconded, with two pieces of #8 wire.
Birds could easily cause the spread of fish. Ever squeezed a fish that's stuffed with eggs when you pick it up. So a large predatory bird picks up a pregnant fish of a size it can't gulp down. While taking the fish to it's nest it flies over a pond... And there's your legend.
Many things in nature - appear out of nowhere, but there is always a rational explanation.
Dousing, witching, I'm sure it's an energy flow thing. I can't do it but I won't dismiss those who can.
