In the Matsya avatar story, Vishnu warns King Manu about an approaching deluge. The fish incarnation first appears as a small fish seeking Manu’s protection, then grows miraculously large and reveals the danger of the flood.
Matsya instructs Manu to build a boat and gather seeds, living beings, and the seven sages, depending on the textual version. When the waters rise, Manu fastens the boat to Matsya’s horn, often using the serpent Shesha as a rope, and the divine fish guides it to safety near the Himalayas. Manu then becomes the ancestor and lawgiver of a renewed human world.
The story changes across Hindu literature. The earliest surviving account, in the Shatapatha Brahmana, does not clearly identify the fish with Vishnu. Later epic and Puranic versions connect Matsya with Brahma or Vishnu, and some emphasize the rescue of the Vedas as well as survival from the flood. “Manu” can also be a title for a successive cosmic progenitor; this episode commonly concerns Vaivasvata Manu.