Once when the River Don was in flood, a man needed to cross it to attend a relative’s deathbed. The river had a resident Kelpie, a dangerous water-spirit which could, however, appear helpless or even helpful. This creature appeared and offered to carry the traveller across the swollen stream; the man agreed, but when they got to the middle of the river the Kelpie tried to drown him. Luckily he managed to escape and scrambled up onto the riverbank. Baulked of his prey, the angry Kelpie threw a large boulder after him, which still rests on the bank and is still known as the Kelpie’s Stane.
The Lore of Scotland : A Guide To Scottish Legends
Westwood & Kingshill