At the end of the past millennium, at the end each of Brahmā’s day, because Lord Brahmā sleeps during the night, annihilation takes place, and the three worlds will be covered by the water of the ocean.
Sanatana Dharma – The Eternal Truth
At the end of the past millennium, at the end each of Brahmā’s day, because Lord Brahmā sleeps during the night, annihilation takes place, and the three worlds will be covered by the water of the ocean.