[Freedom4US]

It isn’t as if this was some remote deep water lake, it was clearly visible just yards from a nice home and recently cut grass. Seems pretty strange to me at a quick glance.

[bigbob]

Well, from the image it looks to me like while it’s obvious from above, it might not be visible from an oblique angle from one of the houses. But everybody likes to Google Maps search their neighborhood and I suspect it jumped out at him when he did.

[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.