This is about Lake Cerknica - the largest lake in Slovenia, when its there, of course, part of the Notranjska Regional Park . When its there its about 25 km2, but can reach up to 38 km2. It has a complicated system of communications with the underground reservoirs which means the lake can drain and thus completely disappear. It usually fills up after the autumn rains and the spring thaw, and is empty round May and June (sometimes even in winter) so I was lucky to see it when I was there on June 16th. It has been recorded the lake draining off and not re-appearing for a whole year.
By the way, if you open Google maps and look up Lake Cerknica, you will see the aerial view of it when it is drained.
On of the problems with this lies with the local fish. Now imagine you being a fish and your whole world that you know gets drained once or twice a year, like down a toilet. You have to appreciate this being a bit of a existential problem for the poor fish. There is, however, a system in place for protecting these poor fish by capturing/keeping them in a part of the lake that doesn’t get drained.
For all you bird-watchers out there you would be interested to know the Cerknica lake is an important habitat area for over 250 species of birds, about a hundred of those species nest here. A few of them are very rare and on the endangered list like the Corncrake , Common Snipe , Red-necked Grebe , Ferruginous Duck , Northern Shoveler , Common Redshank and the Curlew .