Interesting; Google Earth maps as recently as June 2015 don't show any structures up slope from that area and certainly none with water.
It’s not a structure, not like a dam that you would imagine. It’s a catch basis and in dry season or even a reasonable rain would just look like a field, dip in the ground.
We’ve just had a very abnormal amount of rain. If we get some wind in it will start to dry things out.