Source: The St. Lawrence Seaway Authority and Saint Lawrence Seaway Development Corporation.
Note: Before 1999, coal tonnage was part of bulk.

Composition of the Traffic Transiting Through the St. Lawrence Seaway, 1978-2011

The traffic handled by the seaway is dominated by bulk cargo (iron ore and coal), with general cargo accounting for only 4.4% of the total tonnage. This implies that the great majority of ships using the seaway are bulk carriers. The Seaway is also an important gateway for the export of North American grain on global markets.