The Wall may have gone and the buoys that marked the state boundary on the Great Glienickersee been washed away, yet an invisible frontier persists. On the side that used to be East Germany, there is talk of putting out the buoys again.
The fishing licences already come with a map. The lake is not as big as its grandiose name would suggest - a mile long and perhaps 500 yards across at its widest - but a dotted line runs through the middle. On one side, all the water and all the creatures in it are the property of Mr Ludwig, the third generation of Ludwigs farming the lake. The other side once stood in the German Democratic Republic, but its anglers could not get to the lake because of the wall and watch-towers enclosing it.
And then the Wall fell. Suddenly, you could hop into a paddle boat and row unhindered towards Mr Ludwig's restaurant. But the lake was not reunited. Mr Ludwig spent the next years trying to lease the waters beyond the former buoys from the newly created Land of Brandenburg. When the tender came up in 1997, he bid 200 German marks (pounds 68) per hectare per year, about four times the going rate. He lost. The winning bid, still to be enumerated, came from the Anglers' Association of the former East Germany, represented by the head of the local angling club, Rudolf Schneider.
Mr Schneider used to work in a lamp factory, but now he runs a restaurant. It happens to be next to Mr Ludwig's, but no road connects them, so a visitor in search of culinary variety has to round the lake to get from one place to the other.
Mr Ludwig catches and cooks the fish he serves to his up-market clientele. Mr Schneider does not fish. He serves up meat-balls.
Mr Ludwig swims in money while Mr Schneider struggles, but that is immaterial. The members of Mr Schneider's angling association all have the right to try catching the monster that lurks in the Great Glienickersee, whereas anyone who wants to have a go on Mr Ludwig's side has to pay him for the privilege. This conflict is about the collectivism of the East versus the individualism of the West, and never the twain shall meet.
Mr Ludwig continues to stock the lake, as his family had done since 1945 - a lake now filled with East German anglers scouring the depths for the legendary pike-perch. "This is all political, because I'm a Wessi," he says. "They always think we want to take something from them." All he wants, he insists, is that 30-pounder.