Are you in the U.S.? What's your elevation on the lake?
Is the lake on a faultline--such as the Great Lakes or
near the New Madrid Fault? Would need more info.

Pretty much you have to begin to research
all of the material that is currently out there about
"Earth Changes" (You can even google that phrase and
you'll find tons!) Mainly the oceans, the Gulf of
Mexico, find out if the river that feeds the lake
is on a fault system (many larger rivers, like the
Mississippi sit right on top of faults--that's why
there's water there! lol!)

And as far as why? Read the material I've provided in
the intro page. That's good for a starter.
And, please, you guys...I'm NOT TELLING anyone
what they should do in their individual cases. I'm
only trying to get the word out that if "ReadyDOT.org"
is putting out videos that show people turning
up-side down they are trying to get a subtle message
out that things are changing and to have a
"heads-up" in your own areas. You make your own
choices with the information available to you.
The first HUGE STEP is LOOK AROUND YOU--most folks
aren't even to that point yet!
Cheers!
SK