Asylykul, Karst lake in Bashkortostan, Russia

Asylykul is a karst-collapse lake in Bashkortostan, the republic's largest, with a surface area of 23.5 km², a length of 8 km, a width of 5 km and a maximum depth of 5.1 m. It lies in a broad basin between the Ulutau, Tubuldak, Ulu-Karagach and Belekey-Karagach peaks and the spurs of the Tashlytau ridge, built of carbonate sandstones. The southern shore is a steep slope rising from 210 to 370 m, cut by gullies and stepped by a structural terrace 50–300 m wide, 10–30 m above the water. The water is slightly saline and highly mineralised.

The lake is karst, formed when gypsum and limestone dissolved and the roof of a cavity collapsed. The Bashkir epic "Zayatulyak and Khyukhylu" is set at Asylykul. In 1833 Vladimir Dal recorded the legend that the lake rises and falls before misfortune. Its water is slightly saline, not fresh.

The name comes from the Bashkir asyly, "forked", and kül, "lake"; a Bashkir tale instead explains it as the "angry lake", and Vladimir Dal recorded the form Assuly in 1833. Bashkirs say the lake has a master who leaves the water and sits on a stone, warning of coming misfortune. The lake appears in the epic Zayatulyak and Khyukhylu and in the song Asylykül.

The lake is accessible from several nearby villages through local roads that connect to the main regional highway. Visiting is easiest during warmer months when the water is ice-free and the surrounding area is not muddy.

The lake's water is hard, salty and of the sodium-sulfate chemical class, and its level rises and falls without obvious cause. Vladimir Dal, who travelled the Bashkir lands in 1833, recorded that locals took a sudden rise as a warning of misfortune. The Bashkir name is explained as asyly, "forked", plus kül, "lake".