The city of Trollhättan is located at the western end of the great lakes in Sweden. The location close to the lakes and not too far from the sea meant there was a demand for building canals to make it possible for the swedes to have an inland canal route through the country so they didn’t have to pass through the Danish controlled waters of The Great Belt and Øresund when they were travelling from the Baltic harbors of Sweden to the harbors on the other coast.
The original canals were rather small since they should only accommodate fairly small ships sailing through them. So if you head for the old locks in Trollhättan you will find some old locks which look very tiny and only small boats can pass through them. These old locks date back to around 1800.
In the 1830s Sweden made a giant building project making the Göta Canal which should allow large ships to use the inland route through the lakes and canals in Sweden. This new large canal would allow much larger ships to travel through the route. The old lock was no longer sufficient to let the large ships through. The old locks were replaced by bigger locks.
The old canal is actually still in use and during our stay in Trollhättan we saw large ships sailing though the locks in the center of the city. It took a while for the ship to get through a lock and the bridge which had to be opened stopping the traffic. But apparently it is still worth the wait for the shipping since it saved a long trip on several trucks if the cargo ships had to be replaced.