Which one of the following is an artificial lake?

The correct answer is A) Kodaikanal. The Kodaikanal lake was created in 1863 when a marshy valley was dammed. Sir Vere Henry Levinge, then Collector of Madurai, had the work done, so the lake is man-made.

Why the others are natural lakes:

• Kolleru (Andhra Pradesh) is a natural freshwater lake lying between the Krishna and Godavari deltas. It is a Ramsar wetland, and aquaculture encroachment has shrunk it over time, but it was not built by damming.
• Nainital (Uttarakhand) is a natural lake in the Kumaon Himalaya, formed in a basin of natural origin. The town's popularity as a hill station makes it look artificial, but the lake is not.
• Renuka (Himachal Pradesh) is a natural lake in Sirmaur district, associated with the Parshuram legend, and is the largest natural lake in the state.

Core concept: the distinction between natural lakes (tectonic, glacial, oxbow, lagoon) and artificial lakes (reservoirs and impoundments). For Mains, the same topic links to wetland conservation, eutrophication and the Wetlands (Conservation and Management) Rules, 2017.

Trap: aspirants assume that a lake in a hill station or a tourist town must be man-made, or they guess from the name. Check how the lake was formed, not where it is.