Long Lake, or Chang Hai, is the largest lake in the Jiuzhaigou Nature Reserve in the northern Sichuan province of southwestern China.
It is 3,102 m (~10,177 ft) above sea level and curves in an S-shape, across a length of 7.5 km (~5 mi) and covering a total area of around 0.93 km2 (0.36 sq mi). It reaches in places a depth of 80 m (~262 ft), with a maximum recorded depth of 103 m (~337 ft). As with many of the lakes in the area, it has high concentrations of calcium carbonate, and its waters are beautifully clear, so rocks on the bottom are visible even at high depths. Where other lakes in the park are green and turquoise-colored, Long Lake is a rich, sparkling blue.
At the coldest times of year, ice on the lake can form up to 60 cm (23.6 in) thick, so thickly that even a truck can drive on it.
Surrounded by green hills, and snow-capped mountains from autumn onwards, the lake is quite beautiful. A viewing platform allows visitors to look down and across the lake and steps lead down to the lakeside, but it’s not permitted to touch the water. The area can get very busy in peak season.
There are no visible tributaries going into or out of the lake – the water it gains is through snow melt and is lost through evaporation and seepage. It is known locally for neither running dry in winter and spring nor brimming over its banks in the wetter rainy and autumn. This is why local Tibetans call it “a magic gourd that will never be poured full or dried up”.