Cave diving down in Florida we would hit these spots where the water was covered in "duck weed". It was all green and stuck to you a bit, looked horrible, but it was just on the surface and you would have this crystal clear spring water just under it. If a turtle stuck its head up it would look like this picture.
everyone is right except Gary, NOT mother in law --- ex wife!
seriously, this was one of the absolute largest Snappers I have ever seen. back in the day when I was shooting with something very different if we dropped a crow in the pond it wasnt very long at all that we would see the blob come up within a foot of so of the bird and then disappear . within seconds you would see crow twitch even though dead and then just gone under the duckweed. Nature at work! kind of like the opening scene of jaws.