Panorama Photo

SOLVED RIDDLE.

Lake Doberdò (Lago di Doberdò) is one of the few karst lakes in Europe.

Its water level varies with the levels of the Vipacco and Isonzo rivers (distant some kilometers and communicating with the lake through natural underground tunnels). During the drier periods, its water level drops and the lake surface is reduced to canals and small pools. This particular hydrological regime is characteristic of karst lakes, which alternately undergo flooded periods (generally in spring and autumn) and dry periods (winter and summer).

In this photo you can see the lake in the dry regime. It is the same lake ;-)
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