It looks like an old bath tub full of greenish water, but it's a pond. A few weeks ago, F dragged it out into the vegie garden paddock and we filled it with soil, planted three water chestnuts, then flooded it. The water chestnuts didn't look too fantastic after travelling here by Australia Post - the one on the far end had three reeds, two of which were broken, which barely reached the surface of the water. Since they went in, they've thrived.
The plank poking out the end of the tub is for frog access. While I haven't spotted one yet, I've seen a lot of large bubbles rising through the water, so I'm hopeful. I'm currently waiting for some azolla (a native water fern) to arrive in the mail, which will both provide cover for frogs and reduce surface area for wrigglers to breed in. I'm also expecting some kangkong seeds in the mail, to add to the edible aquatics. I'll probably plant something around the outside of the tub to disguise its sides at some point, too.
I'm a bit hesitant to put any fish in there if the frogs don't turn up and we need to keep mosquito larvae under control... I could probably provide enough cover from birds and such, but I'd be worried about temperature fluctuations and water levels. It seems to me to be a safer place for something amphibious. Eventually, I'd like a larger ornamental fish pond somewhere... and F is very interested in having an aquaponics setup for fish to have for dinner.