well, in this area it probably hidden underground and fills up seasonally. I didn't introduce this object, just edited park

Dear Marios!
Please stop assigning the "name=building" tag to buildings you draw as it is needless. Also please remove these names where they're exist.
building=yes is enough on a first stage. Also you may want to refer osm wiki for more relevant instructions.
In addition - recently you've marked the whole island as building=yes and whole Cyprus appeared to be as a single house in OSM! So please, be careful in your edits