(W). Western freight vessels could stop only at dedicated service areas, because the East German government wanted to prevent any East Germans from boarding them. Through these waterways, West Berlin was linked to the western European inland navigation network, connecting to seaports like Hamburg and Rotterdam, as well as to industrial areas such as the Ruhr Area, Mannheim, Basel, Belgium, and eastern France. In July and August 1945, the Western Allies and the Soviet Union decided that the operation and maintenance of the waterways and locks, which were previously run by the national German directorate for inland navigation (), should be continued and reconstructed in all four sectors. Except for the originally city-owned Neukölln Ship Canal and some canals built later (e.g. Westhafen Canal) and locks, West Berlin had no separate inland navigation authority, but the East Berlin-based authority operated most waterways and locks, their lockmasters employed by the East. Because of their negligent maintenance, the western Allies later transferred their control to the Senate of Berlin (West). The western entrance to the Teltowkanal, connecting several industrial areas of West Berlin for heavy freight transport, was blocked by East Germany in Potsdam-Klein Glienicke. Therefore, vessels going to the Teltowkanal had to take a detour via the river Spree through West and East Berlin's city centre to enter the canal from the East. On 20 November 1981, East Germany reopened the western entrance, which required two more vessel border checkpoints – Dreilinden and Kleinmachnow – because the waterway crossed the border between East Germany and West Berlin four times. Another transit waterway connected West Berlin via the East German vessel checkpoint at Hennigsdorf and the Oder-Havel Canal with the Oder river and Polish Szczecin (Stettin). Air traffic Air traffic was the only connection between West Berlin and the Western world that was not directly under East German control. On 4 July 1948, British European Airways opened the first regular service for civilians between West Berlin and Hamburg. Tickets were originally sold for pounds sterling only. West Berliners and West Germans who had earlier fled East Germany or East Berlin, and thus could face imprisonment on entering East Germany or East Berlin, could only take flights for travel to and from West Berlin. To enable individuals threatened by East German imprisonment to fly to and from West Berlin the West German government subsidised the flights. Flights between West Germany and West Berlin