How Was Lugu Lake Formed? The Geology Behind Its Blue Water

Why is Lugu Lake water so blue? Why is it a highland lake? It all starts with the geology of the lake basin.

Lugu Lake is a fault lake

Lugu Lake is not an ordinary lake – it is a fault lake, formed when the earth's crust broke and subsided.

About 20 million years ago, crustal movement in the Hengduan Mountains was violent. The rock layers here fractured: one side rose while the other sank. The sunken block became the basin of Lugu Lake.

That is why the lake is exceptionally deep – an average depth of 40 m and a maximum of 93 m. Deep lakes like this are rare across China.

Where does the water come from

The water of Lugu Lake comes mainly from groundwater and precipitation.

Groundwater: the surrounding mountains are limestone. Rainwater seeps into the rock and emerges as springs feeding the lake. This is why the water is so clear – groundwater filtered through limestone carries very few impurities.

Precipitation: the Lugu Lake area receives about 1,000 mm of rain a year, most of it in summer. Rain falling directly onto the lake is another source.

The lake's outflow is on the east side, the Langfang River, which joins the Jinsha (Yangtze) River.

Why is the water so blue

Three reasons:

First, it is deep. When water is deep, sunlight penetrating the surface has only blue light scattered back; red and orange light are absorbed. The deeper the water, the bluer it looks.

Second, it is clear. The water transparency of Lugu Lake reaches 12 m. The clearer the water, the more fully blue light is reflected.

Third, there is no pollution around it. There is no industry near Lugu Lake, little agriculture, and few impurities in the water. If the water were murky, no depth would make it blue.

Put these three together and you get the distinctive blue of Lugu Lake.

How did the islands form

Lugu Lake has seven islands; the two largest are Liwubi Island and Xieva'e (Tsaiyao) Island.

They are all products of fault uplift – when the basin subsided, some spots did not sink completely and remained above the water, becoming islands.

Liwubi Island has a lama temple and is the most famous island. Xieva'e Island is where Joseph Rock once lived; the buildings there today are later reconstructions.

What is the altitude of Lugu Lake

The lake surface is at 2,690 m.

This is not high, and most people will not have altitude sickness. But if you climbed Jade Dragon Snow Mountain (4,500 m) the day before and then drive to Lugu Lake the next day, you may feel unwell from fatigue and carsickness combined. That is not altitude sickness – it is exhaustion.

Does Lugu Lake freeze in winter

No.

Although the lake is at altitude, it is a large body of water with huge volume, so it never completely freezes. Only in unusually cold years does thin ice form in shallow bays.

This is one reason winter at Lugu Lake is attractive – the lake stays open, and migratory birds fly in to winter here.

Will Lugu Lake disappear

Not in the short term.

Lugu Lake is mainly recharged by groundwater, so its volume is stable. As long as the surrounding mountains are not damaged and groundwater keeps flowing, the lake will not dry up.

But over the long term there are two risks:

First, pollution. After tourism development, untreated sewage discharged into the lake would degrade water quality. This is why Lugu Lake has been carrying out environmental demolitions in recent years – lakeside guesthouses have been removed and moved 80 m back from the shore.

Second, siltation. If soil erosion carries sediment into the lake, it shallows. This is why the surrounding vegetation must be protected.

Lugu Lake is a gift of nature. How to protect it is the responsibility of our generation.