Very dubious sounding but there you are.
The etymology of Echt is not known with certainty. An old tradition refers it to the Gaelic word “Each,” which signifies a horse. It bears that a division of an ancient Caledonian army having encamped in this parish, the officers and men, in the time of a severe drought, were reduced to great straits for want of water, when a horse which had been brought to the camp was seen to gallop to a spot where he had been accustomed to drink; and that, by pawing and scratching with his feet, some signs of water were discovered; in which spot, a well having been dug, afforded relief from thirst to the army. In memory of that event, this particular district, and afterwards the parish, is said to have been designated by the above term.
This from the New Statistical Account, by the Rev. William Ingram.
I can understand why you think that is dubious, the River Don can't be more than a mile from the Barmekin, going past Old Keig RSC.