Lake aging is the natural process by which a lake fills in over geologic time with erosional materials carried in by tributary streams, with materials deposited directly from the atmosphere, and with materials produced within the lake itself.

Limnologists (lake scientists) use several high-tech methods to determine a lake's age, primarily through sediment core analysis. By drilling deep into the lakebed and extracting a vertical column of mud, scientists can count varves, which are annual layers of sediment similar to tree rings. They also use radiometric dating, such as Lead-210 for "young" lakes (under 150 years) and Carbon-14 for older ones (up to 50,000 years). In 2026, tephrochronology is increasingly used, where distinct layers of volcanic ash from known historical eruptions act as "time markers." For ancient "rift lakes" like Lake Baikal or Lake Tanganyika, which are millions of years old, researchers use paleomagnetism—measuring the alignment of magnetic minerals that locked into place whenever the Earth's magnetic poles flipped. This combination of "absolute" and "relative" dating allows scientists to reconstruct the entire history of a lake's formation and climate changes.