Well the Inca flood myth derives from the more primitive Andean cultures who talk about some form of great flood at least 4,500 years prior. This is the Caral culture who was on the other side of the Andes, 600+ miles away from Titicaca. So while its likely they were aware of Titicaca, its probably unlikely that they lived around it to experience flooding. However, their culture was founded around the city of Huaricanga which was only 10 miles away from the Pacific Ocean. So whatever flooding they might have experienced would have likely been from the Pacific ocean, not Titicaca.
The timing of the myth itself puts it roughly in same time frame as Sumerian flood myth, the earliest mention of which is written by Sumerians about 4,000 years ago (but the flood happened some time earlier). So the timing is very close. Mayans have a flood myth that supposedly emerged around same time, though that just might be timing with emergence of their culture around same time.
I've seen this theory more than a few times and it matches up well timewise and location wise to the various flood myths that unconnected cultures started establishing around the same time
The universal human myth may be the first example of disaster reporting.
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