This is a method that has been in use since the Middle Ages, when the monasteries and the nobles had the bright idea of using valley bogs that would have been of no use otherwise as handy receptacles for fish-farming. All you needed was a stream running through a boggy valley that was naturally formed like a bowl, and a retaining wall at one end, with a sluice to let the water out. This ensured a constant replenishment of fresh water for the fish. In a land-locked country, that meant that there was always a plentiful supply of carp - and if you look at the map of Southern Bohemia, you will see it woven through with blue, a true tapestry of lakes; especially around the town of Trebon - an amazing feat of mediaeval engineering where the massive ponds are interconnected with channels that act as conduits between them.
Olsina lake is not part of such a complex web, it is a pond on its own. But at 167 hectares, there is a lot of room for fish, and if the last harvest is anything to go by, we have much to look forward to: on Wednesday at dawn, we shall watch the fishermen use the same methods that their counterparts have been using since the 14th century - apart from the lorries that will carry the tanks with live fish away. But one can imagine the heavy carts of old, the strong horses, the large wooden tubs ... after all the fish need to be kept alive and well till Christmas! Because the main reason for the big harvest is that carp are THE Christmas fare for the Czechs, as they have been as long as memory can reach.
Well, I shall be there to watch the spectacle, and take some photos to share the day with you.