There was no worldwide flood in recorded human history.
And an understatement to be sure, no evidence of worldwide flood found for a long time before that!
But the problem is people are free to teach and believe whatever nonsense they want: that the earth is hollow, that there are human vampires that are undead (I don't mean weird goths who drink a little blood for mental reasons), or that grey alliens are abducting people and giving them rectal exams.
I mean I'd love to go to all these people and set them straight but you know any efforts in that direction would just more deeply convinced them of a conspiracy. The thing about the paranoid capacity of the human brain is that it can fit anything into a system if it's motivated enough.
After all science is just Satan's attempt to hide the truth revealed in the Bible don't cha know. All that evidence was just dummied up by the devil to deceive those who don't have spiritual sense. Once you believe that then it's easy to believe all the other stuff. And people routinely believe just those sorts of things.
In fact it appears much easier for many humans to believe that sort of stuff than it is to believe that the square root of 2 is irrational, or that nothing can go faster than the speed of light. Those are things we have very good evidence for but it's hard for the brain to grasp. Some how allien rectal exams or talking snakes or a world wide flood seems quite reasonable to many people.