Asked by: Ellie Pearson, Northampton
This title goes to 1,642m-deep Lake Baikal (pictured), which is located in southern Siberia. As the water in Lake Baikal is very clear it is possible to see to a depth of 40m from the surface.
The lake is part of an ancient rift valley, and has formed as the planet’s crust slowly pulls apart in that area. It contains around one-fifth of the world’s unfrozen freshwater reserves.
Its isolation and age have led to the evolution of an unusual ecosystem, containing many plants and animals that are unique to the area. When winter rolls around, a thick layer of ice can form on the lake’s surface, trapping streams of bubbles released from algae living in the chilly depths.