1. The sea water had risen significantly, and a rare astronomical phenomenon occurred, unknown and unobserved by them. The lunar nodes, i.e. Rahu and Ketu are no longer moving in their retrograde motion, which means that moon has stopped changing the orbit, with reference to the apparent path of the Sun. This has resulted in cession of wave movement. The so called churning of sea water has stopped. Rahu and Ketu are dead. Another demon(or in scientific language, a set of astronomical points) in the next Kalp will step in to replace the dead Rahu and Ketu during Kurma Avatar of lord Vishnu in the next Kalp. The wave movement will then once again start. But that is going to happen in the next Kalp, which was least 250,000 years away from the start of the transitional phase.
2. 250,000 years is a long time by any standards. The survivors had had no knowledge what they were into. Initially they had enough provision with the assumption that it was only a temporary phase. But now when the wave movement had also stopped, they started having the uneasy feeling that they were into something more difficult. True they were the lucky ones, because of the resources, they had survived the great flood, but they had no idea as to what next?
3. The first problem now these survivors were facing was the depletion of provisions, which was no longer available anywhere. They could anchor, as some hill top, as land, were still there, but what little information they were getting from friendly ships was that there the people were fighting amongst themselves, killing each other, and looting. Humans had never learnt the art of sharing. However human is the most perfect creation of God, which can find ways to survive in extreme difficult circumstances.
4. Now several generation or a few hundred years have passed. The ships were now less sophisticated, as they did not had the necessary infrastructure available earlier in Kalyug. Survivors do tell each other how their forefathers enjoyed life with lot of wonderful gadgets, but that looked more like a story and belief.
5. These ships organized themselves into groups to help each other as far as possible, as survival was difficult without help. This also helped them in combating the threat of other ships that may have aspiration to loot and capture their ships.
6. Now the current generation did not even know how many thousands of years have passed after the great flood. They know they have to venture out in sea because even now sea food was the only food available to them and like their forefathers; they also worshipped fish as an avatar of Vishnu. True they could anchor at land from where they do not venture out very far, but then they knew they were safer in sea because they were in a position to avoid unfriendly guests from other ships, which was not possible on scarce land.
7. Most of these ships were in the seas of what was earlier Indian sub continent, as this was the only region where sea food was available and the weather was such that survival was relatively easy. It is in this context Matsya Avatar is to be visualized. Although during these thousands of years intermingling did happen but not all the ships could be classified as friendly.
8. Some ships exclusively contained persons who would attack to capture humans for killing and eating and they were termed Rakshas. Since the time was abnormal, abnormal rules were made for Survival of the Fittest. It is in this context MANU Smriti is to be accepted. The word Manu clearly indicates that survival from all breeds of men from all over the world were represented by the chief or King who could call himself Manu, representing man, manushya etc etc.
9. Now slowly and almost regularly they started seeing wave movement in the sea resulting in increase in land and receding of sea. They now decided to stay on land as they felt they could defend themselves. The tortoise or Kurma which they felt brought this change was hailed as an Avatar of Vishnu.
During their long jurney over sea, they were told to accept this as TRUTH, that their forefather used to live over land and their plight of living over sea, too, will end. and now they had achieved just that; they were living over land. So what they were told and most of them didnot believe earlier was TRUE.....and in their wisdom they called it SATYUG.