Five Flower Lake — Rize Valley, Jiuzhaigou, Sichuan

The first thing to understand about this lake is that you are looking straight through it. Five Flower Lake — Wǔhuā Hǎi, in the Rize Valley of Jiuzhaigou — is shallow, and its bottom is criss-crossed by ancient fallen tree trunks that lie there in plain sight, tilted at every angle like a collapsed scaffold. The water above them shifts from pale jade at the shallows to a deep blue-green where the bed drops away, and none of that colour comes from dye or algae bloom alone. The lakes of Jiuzhaigou were dammed by rockfalls and glacial debris and then set in place by carbonate deposition; the water carries so much dissolved calcium carbonate, and is so clear, that the bed stays visible even at depth.

Jiuzhaigou means "nine settlement valley," after the nine Tibetan villages strung along its length, seven of which are still lived in. It sits at the southern end of the Minshan range on the edge of the Tibetan Plateau, about 330 km north of Chengdu, and it is shaped like a Y: the Rize and Zechawa valleys run in from the south and meet to form the Shuzheng valley flowing north. The area was barely known outside the region until a 1975 forestry survey led to logging being halted and, in 1980, to the creation of the Jiuzhaigou Nature Reserve. It opened to visitors in 1984, was inscribed by UNESCO as a World Heritage Site in 1992 and became a World Biosphere Reserve in 1997. Roughly 300 square kilometres of the core scenic area are old mixed forest, which is why the slopes in this photograph have gone yellow and orange — autumn is the season people come for. The valley is also home to about 140 bird species, and to very small, isolated populations of giant panda and golden snub-nosed monkey.

As a jigsaw it splits cleanly into three jobs of very different character. The sky and the far ridgeline are the easy opening — blue above, a hard silhouette edge below. The autumn forest is the middle game and the most forgiving part of the frame, because the yellows, rusts and dark conifer greens sit next to each other in distinct blocks you can sort by colour before you ever try to place them. The water is the real work, and the trick is to stop looking at colour there and start looking at line: the sunken trunks run in long straight diagonals across the lake bed, and matching the angle and thickness of a submerged log is far more reliable than trying to tell one shade of green from another. Build the shoreline first, then follow the trunks inward from it.