Why Is Lugu Lake Water So Blue? Source, Clarity and Water Quality

People seeing Lugu Lake for the first time are struck by its blue. It is not an ordinary blue – it is deep, translucent, like a jewel.

Many ask: why is Lugu Lake water so blue? Where does it come from? How good is the water quality?

How clear is the water

According to measured data in the book Lugu Lake: Regional Habitat and Cultural Evolution:

Water transparency: 6.0–11.5 m
Maximum depth: 93.5 m
Average depth: about 40 m
Lake area: 48.45 km²

What does 6–11.5 m of transparency mean?

Standing on the shore, you can see 6 m down into the water. On a good-weather day, you can see 11 m. Among China's freshwater lakes, this is top-tier quality.

For comparison:

Lake Taihu transparency: under 1 m
Dianchi (Kunming) transparency: under 1 m
Erhai (Dali) transparency: 2–3 m
Lugu Lake transparency: 6–11.5 m

Lugu Lake ranks in the top three for water quality among China's freshwater lakes.

Why is the water so blue

Several reasons combine:

1. Deep and clean

When water is deep and clean, sunlight hitting the surface loses its red and orange wavelengths to absorption; only blue light is scattered back. The deeper and cleaner the water, the bluer it looks. The same physics makes the sky blue.

2. Very little sediment

Lugu Lake has very few inflowing rivers, and they are all short. According to measured data, only two larger streams enter the lake:

Shekua River on the east shore
Sanjiacun River on the south shore

The rest are seasonal creeks and surface runoff. Short inflow streams carry little sediment, so the water stays clear.

3. Little human pollution

There is no industry around Lugu Lake, little agriculture and a small population – only tens of thousands around the whole lake. Most domestic sewage is treated; very little enters the lake directly.

4. Aquatic plants purify the water

Lugu Lake is rich in aquatic plants, such as the wavy-leaf Ottelia (Haicaihua). This plant demands extremely clean water and only grows where water is very pure – and it purifies the water itself.

Where does the water come from

Many assume Lugu Lake's water flows from Jade Dragon Snow Mountain. Not so.

According to geological surveys, the lake has three main water sources:

1. Rainfall (main)

The lake area receives about 1,000 mm of rain a year. Rain falling directly on the lake, plus runoff from the surrounding slopes, is the main source.

2. Groundwater (secondary)

Many springs surround the lake; groundwater seeps from cracks in the mountain and joins the lake. This water is very clean – in effect high-quality mineral water.

3. Two small rivers (small share)

The Shekua and Sanjiacun rivers carry little water combined.

Where does the water go

Lugu Lake is a semi-enclosed lake; its outflow is on the east shore.

During the rainy season (June–November), the water level rises and surplus water leaves through the eastern outlet, flows through the Yalong River, and eventually joins the Jinsha (Yangtze) River.

In the dry season the outlet dries up, and Lugu Lake becomes a closed lake.

The ten-year fishing ban: cleaner water

Few visitors know that Lugu Lake has enforced a ten-year fishing ban since 2017.

Before that, fishing was practised at the lake; fishermen had worked the waters for generations. But overfishing plus tourism development depleted the fish and degraded the water.

In 2017 a complete fishing ban came into force and all fishermen were moved to other livelihoods. A decade later the results are visible:

More fish in the lake
Better water quality
Clearer and bluer water

Today you cannot eat wild Lugu Lake fish. The fish served in restaurants are farmed, brought in from outside.

Can you drink the lake water

People often ask: the water is so clean – can I drink it directly?

Theoretically, Lugu Lake water meets China's Class I water standard and could be drunk directly.

In practice, it is not recommended:

1. The lake contains aquatic organisms – possible bacteria

2. Visitor activity at the shore – possible pollution

3. Drinking untreated water can cause stomach upsets

Boil it first, or buy bottled water.

Why is the water so well protected

Several factors keep Lugu Lake's water quality high:

1. Environmental demolition

Around 2018, all lakeside guesthouses and restaurants were removed and relocated 80 m from the shore. Previously some buildings stood right at the water's edge and discharged sewage directly into the lake. Now all are gone and sewage is treated centrally.

2. Waste sorting

Villages around the lake practise waste sorting; rubbish is trucked out for treatment instead of being dumped into the lake.

3. Boat limits

The number of pig-trough boats is limited. Fuel-powered boats are banned outright – only hand-paddled pig-trough boats are allowed.

4. Visitor caps

Visitor numbers are controlled; in peak season the lake limits entry to reduce environmental pressure.

Summary

Why is Lugu Lake water so blue? Because it is deep, clear and clean.

Transparency of 6–11.5 m, maximum depth of 93.5 m, Class I national water standard – Lugu Lake is top-tier among China's freshwater lakes.

This is not accidental; it is the result of years of environmental management – from demolition of lakeside buildings to the ten-year fishing ban, from waste sorting to boat and visitor caps. Every measure protects this body of good water.

So when you visit, please protect the environment too: do not litter, do not pollute the lake. This good water was hard-won.