Why did diesel tugs replace stern-wheelers on the Mackenzie River after 1945?

Following World War II, the flat-bottomed stern-wheelers that had operated on the Mackenzie River between 1920 and 1940 were replaced by small diesel tugs.1

This transition occurred because diesel tugs offered greater operational efficiency by allowing a single power unit to push several barges simultaneously. This method, known as a push tow, is particularly advantageous on natural rivers, as it increases the capacity for transporting goods in larger, grouped units.12