While there are multiple versions of this story, the underlying theme and the events associated with the Matsya avatar stays the same in all of them.
One day while bathing, Satyavrata (also called Manu by some) accidentally catches a small fish in his hands. To his surpise, the fish looks at him and starts talking to him. It asks Manu to save its life and protect it in return for which the Matsya will protect Manu from an impending flood about which it is aware of.
When Manu agrees to help, the fish first asks him to put it in a jar of water, and then when it outgrows the same, it asks him to dig a pit, fill it with water and put it in the pit. Later, when it outgrows the pit, it asks Manu to transfer it to the ocean, by which time it is big enough to survive and is also indestructible. At this point, the fish asks Manu to build himself a boat and be ready for the impending flood. It also instructs him that when the flood waters increase, he should think of the fish that will then come over to help him out.
When the flood begins, Manu boards the boat and then prays to the fish for assistance. The fish then appears and ties the boat to a horn that has grown on its head. It uses the serpent Vasuki as the rope to tie the boat to its horn. The fish then tows this boat to safety and takes Manu to the highest and driest point left on the earth.
It is told that as the matsya swam through the flood waters he discoursed Manu on the various topics and revealed to him the knowledge of the Vedas, Puranas, Samhitas and the Supreme Truth.
Some versions also has the matsya instructing Manu to collect seeds of all types of plants and assembling the saptarishis (seven great sages) on the boat who are then rescued by the great matsya.
This post has been written for Friday Fictioneers Photo Prompt – Nov 1 where the post had to be inspired by the pic below.