It was formed about 10,000 years ago when lava and pyroclastic flows from eruptions of the Kronotsky and Krasheninnikov volcanoes dammed the Kronotskaya River.
[1] The lake drains an area of 2,330 square kilometres (900 sq mi),[1] with the Listvennichnaya, Unana, and Uzon being the largest rivers to flow into it.
[1] The area surrounding the lake is uninhabited and protected as Kronotsky Nature Reserve, a component of the Volcanoes of Kamchatka World Heritage Site.
[1] Massive rapids at the head of the Kronotskaya River prevent fish from entering or leaving the lake.
[2] There are 11 islands in the eastern side of the lake which cover a total area of around 0.5 square kilometres (0.19 sq mi) and host a colony of about 600 pairs of slaty-backed gulls.