The Thread of Gold by A.C. Benson

Very deep in this enchanted land of green hills in which I live, lies a still and quiet valley. No road runs along it; but a stream with many curves and loops, deep-set in hazels and alders, moves brimming down. There is no house to be seen; nothing but pastures and little woods which clothe the hill-sides on either hand. In one of these fields, not far from the stream, lies a secluded spot that I visit duly from time to time. It is hard enough to find the place; and I have sometimes directed strangers to it, who have returned without discovering it. Some twenty yards away from the stream, with a ring of low alders growing round it, there is a pool; not like any other pool I know. The basin in which it lies is roughly circular, some ten feet across. I suppose it is four or five feet deep. From the centre of the pool rises an even gush of very pure water, with a certain hue of green, like a faintly-tinted gem.

The water in its flow makes a perpetual dimpling on the surface; I have never known it to fail even in the longest droughts; and in sharp frosty days there hangs a little smoke above it, for the water is of a noticeable warmth.