[Hot Tabasco]

That's a very steep embankment, over 45 degrees by the look of it, with murky water plus it's obviously deeper than "just under the surface".

Unless somebody ran into it while swimming, it's understandable why it was never spotted before.

[Freedom4US]

I get that part, it’s just odd there weren’t any periods of drought when water levels receded, swimmers, or maybe an oil slick, all kinds of stuff.