The Welland Canal
To start off it is interesting to note is that the word canal was originally used in the fifteenth century to describe a tubular passage for fluids, and is closely tied to the words channel and cane. In case you were wondering, a canal is man made while a channel is natural. Since ships cannot pass through waterfalls such as those at Niagara, canals were built to connect the Great Lakes with the St. Lawrence Seaway.
Construction started on the first Welland Canal to connect Lake Ontario with Lake Erie in 1824. Workers used hand tools and horses and earned $0.50 per day! The canal connected the lake Ontario inlet and 12 Mile Creek at Port Dalhousie to the Welland River which runs into the Niagara River just south of the falls. To move a ship against the current up a 100 meter high escarpment, or the opposite way, 40 locks had to be built. (A lock is where a ship sits enclosed as the water level is increased or decreased to allow it to move up or or down an incline.) Some parts of the initial canal are still visible, but the original locks were made of wood and have mostly deteriorated.
The freight quickly outgrew the canal so larger canals were needed. By 1932 the fourth, last, and final Welland Canal, was constructed. With time, through the industrial revolution, technical advances grew so much that fewer locks were needed even though the canal itself, and the ships, were much larger than a hundred years earlier. The current canal has only 8 locks and it takes most ships 11 hours to traverse the 44km from Port Weller on Lake Ontario to Port Colborne on Lake Erie. About 3000 ships per year pass through from March to December. In the winter the 8.2m deep canal is drained to allow for maintenance and prevent accidents due to bad weather.
The website ais.boatnerd.com/map has an interactive live map where you can see all the ships in, not just the welland canal, but in the entire Great Lakes - St. Lawrence Seaway. I strongly encourage you to check it out! If you'd rather experience the canal for yourself in your real, there is the option to take your personal pleasure craft tour of the locks for $320.