The port of Trois-Rivières has always benefited from the advantages of its geographical location. But it has also had to suffer from the drawbacks of this very same location on several occasions. Located at the confluence of the St. Maurice and St. Lawrence rivers, Trois-Rivières is the sole port serving both the imports and exports of the whole St. Maurice valley region, whose economy is dominated by heavy industry and forest products. The fortunes of the harbour have therefore always depended upon the economic situation in the St. Maurice valley's manufacturing plants and forest operations. The level of traffic reflects the ups and downs of the regional economy. Located half-way between Montréal and Québec, in the heart of southern Québec, Trois-Rivières suffers up to a point from the competition on the part of both neighbours, which are better equipped, have more space for expansion, and serve larger and more heavily populated hinterlands. Finally, Trois-Rivières had benefited from the opening of the St. Lawrence Seaway in 1959 through the strenghthening of its cereals transhipment function. However, in recent years, it has had to face competition from ports in Eastern Québec and on the Pacific coast, ports which are either better equipped for the handling of grain or better located for the expanding Asian trade in Canadian cereals. The purpose of this article is to analyse the problems of the port of Trois-Rivières. A detailed traffic analysis for the 1961-1970 period based on computer processing (creation of an origin-and-destination data bank) is also summarised here ; the methodology will certainly apply for most Canadian ports.