canal (canals and inland waterways) in north-central Poland that links the Vistula River basin with that of the Oder River. The canal extends for 27 km (17 miles) between Nakło and the inland port city of Bydgoszcz. Construction of the 19-metre- (62-foot-) wide canal and its eight locks was completed in 1774 under Frederick II, who had annexed the region to Prussia in 1772. The canal was rebuilt between 1905 and 1917, the number of locks between the Brda and the summit being reduced from eight to four. The new locks were 57 metres (186 feet) long and 9.4 metres (31 feet) wide. The new canal was 36 metres (117 feet) wide at water level, with a depth of 2 metres (6.5 feet).