Welland Canal

I will try to explain the process shown in the pictures as best as can and hope that it all makes sense.

This canal connects two of the Great Lakes, Lake Ontario and Lake Erie. This one is called the Welland Canal. At this point in the Great Lakes, Lake Erie is higher in elevation than Lake Ontario. As the ship gets ready to enter the canal a gate opens to let them in. You can't see it in this picture because it is already open but you can imagine where it would be. The ships come into the canal and a lever comes down in front of them to stop them from continuing on. Then the gate behind them closes.

The reason the lever has to come down in front of the ship is because the lakes are different elevations. They are locked in the canal so to speak. When the lever is down and the gate behind the ship is shut, they slowly start to open the gate, not the lever, that is in front of the ship. Gravity slowly starts to pull the water out of the canal which lowers the water level in the canal, making the ship sink down with the water level. When the water level in the canal is the same as the water level in the lake, the lever is moved and the ship can continue its travels. It takes less than an hour for all of this to happen and it's really quite neat to watch.

This is the ship coming into the canal.

This is after they've opened the gate in front of the ship.

This is a bridge being lifted so the ship can get through.

Here is a little information about the Welland Canal from Wikipedia I thought you might find interesting.

The Welland Canal is a ship canal in Canada that runs 42 km (27.0 miles) from Port Colborne, Ontario on Lake Erie to Port Weller, Ontario on Lake Ontario. As part of the St. Lawrence Seaway, the canal allows ships to traverse the Niagara Escarpment and avoid Niagara Falls.

Approximately 40,000,000 tonnes of cargo are carried through the Welland Canal annually by over 3,000 ocean and lake vessels.