Jiuzhaigou is a valley in the mountains of northern Sichuan, China, where more than a hundred lakes step down the slopes in colours from turquoise to gold, each one held by a natural dam of travertine and clear enough that whole fallen trees lie visible on the floor far below. The colours come from the water itself: it is cold, rich in calcium and almost free of silt, so that light goes deep and comes back tinted by the lime and the plants on the bottom. Five Flower Lake is the showpiece, its surface shifting from turquoise to yellow to green within a single pool, with drowned trunks crossing the bed; the trees do not rot, because the mineral water coats them in a crust instead of letting them break down. Long Lake is the largest and highest, in a broad basin with snow-streaked peaks sealing its far end, and Mirror Lake earns its name in the windless hour after dawn, when it holds the forest and the mountains almost flawlessly.
The lakes are joined by falls. At Nuorilang the river slides off a travertine cliff 320 metres wide and drops in a broad, even sheet rather than a single plunge, and a boardwalk runs along its lip; at Pearl Shoal the water races over a wide slope of travertine in a spray of drops that gave it the name. The valley takes its own name from the nine Tibetan villages along it, and the people who still live in a few of them tell the lakes as the shards of a mirror: the mountain god Dago made it from wind and cloud for the goddess Semo, who let it slip and shatter across the valley floor. The summer rains put the falls at their loudest, but the moment the park itself names is 15 to 30 October, when the forest turns crimson and gold and the colour doubles in the mirror-still lakes. In Jiuzhaigou the water is the colour of the season, and the season is best in autumn.