Rankala was dig as a stone quarry before 8th century as there was a massive mine of black stone. According to Wikipedia, the lake was formed naturally due to earthquake happened in between 800-900 AD. During the earthquake, the stones quarry damaged extensively, also some geological changes happened. It enabled the water came out of holes from underground source and gather at surface. Later, the Maharajah Shri Shahu Chhatrapati of Kolhapur built the surrounding structure called Chaupati. He also developed gardens surrounded to lake which added astonishing beauty to it. Before formation of this beautiful creature, there was only stone quarry. That time, a stone structure called as "Rankala." After natural disaster happened, the formed lake was called as "Rankala Lake."