One morning each autumn, on the East Street towpath, a Christmas wreath-like fairy ring springs up next to one of the old wooden pilings. English folklore: cavorting fairies; German tradition: witches; the Danes: devils. The true provenance, though, is stranger still. Neither plant nor animal, fairy rings begin in a tight cluster, ground-level fruit of subterranean tubular hyphae which suck up nutrients til the soil is depleted. With each orbit of the sun, the hyphae pushes into a wider circle as it hunts for new food, creating fairy rings as it does so.
Perennial fairy rings dating back centuries have been recorded. Our fairy ring, unusually, does not expand, but grows thicker each year. It may be that the legion of ducks and geese from the river provide sufficient nutrients for the hyphae to stay put.
A Field Guide to Osney Island 