Blue Lake Cherek

Tserik-Kel, the lower Blue Lake, is only about two hundred and thirty by a hundred and thirty metres across but drops to around two hundred and seventy-nine metres, making it one of the deepest karst lakes in the world and by some measures the deepest of its type. No river runs into it: it is fed entirely from below by a submerged karst system delivering something like seventy million litres a day, and the same volume flows out through an underground channel to the Cherek. The water carries dissolved hydrogen sulphide, which is what gives it the intense blue-green colour and also means almost nothing lives in it. The temperature stays around nine degrees all year and it does not freeze. Cave divers have worked it for decades and the bottom is still not fully mapped; there have been fatalities. From the road there is a viewing area, a path around part of the rim, and a diving base.

What you actually see

• The depth - around two hundred and seventy-nine metres in a lake two hundred across.
• The colour - blue-green from dissolved hydrogen sulphide, not from minerals or algae.
• The hidden feed - some seventy million litres a day arriving through karst channels.
• The constant temperature - about nine degrees year-round, never freezing.

When to go

May to September for the road up the gorge. One to two hours. It is usually combined with the drive on to Verkhnyaya Balkaria.

Honest expectations

Small - the viewing takes half an hour. Diving here is technical, deep and has killed people; it is not a recreational site. Stalls and paid parking at the roadside. Swimming is not sensible given the water chemistry and temperature.

Nearby

The Cherek gorge road continues to Verkhnyaya Balkaria; Nalchik is north.