Fishpond Network in the Trebon Basin

The Třeboňsko region, with the picturesque town of Třeboň at its heart, is unlike the rest of South Bohemia – characterized not by rolling hills but by peat bogs, flatlands and fish ponds. This monotonous marshland, broken only by the occasional Gothic fortress, was moulded into an intricate system of canal-linked ponds as early as the fifteenth century. The fish industry still dominates the region, and around September the ponds are drained to allow the fish to be "harvested". Larger ponds, like the Rožmberk, are drained only every two years, and for several days people from the surrounding district gather to feast, sing and participate in a great local event that's worth seeking out if you're in the vicinity. (source of info)