Labuan Cermin

Danau Labuan Cermin at Biduk-Biduk is stratified: a layer of fresh water sits on top of denser salt water below, the two barely mixing, so a swimmer floats in fresh water and can dive down through a visible boundary - a shimmering layer where the refractive indices differ - into salt below, and taste the difference. The name means mirror harbour, and the clarity is exceptional in both layers, with the bottom visible several metres down. It is fed by fresh springs and connected to the sea by a short channel, which is where the salt comes in. Fish of both fresh and salt water live in their respective layers. Getting there is a long drive from Berau on a road that has improved but remains slow, and Biduk-Biduk itself is a small coastal village with homestays.

What you'll find

• Two layers of water - fresh floating on salt, with a visible boundary between.
• Exceptional clarity - the bottom visible several metres down in both layers.
• Fish in separate layers - freshwater species above, marine below.
• A short boat in - the lake reached by wooden boat from the village channel.

When to go

April to October. Half a day.

Before you go

The drive from Berau is long and slow. Numbers on the lake are managed and it gets crowded at weekends. Sunscreen and soap are banned in the water. Facilities in Biduk-Biduk are simple.

Nearby

Kaniungan and Maratua islands are offshore; Berau is inland.

Key facts