The new waterway will take ships sailing across the Vistula Lagoon from the port of Elblag to the Baltic. Until now, they had to sail round the spit through the Strait of Baltiysk in waters belonging to Russia's Kaliningrad exclave.
Andrzej Duda, the Polish president, officially opened the canal on Saturday afternoon.
The president said that "the opening of the investment... is a great victory of Poland, a great victory of patriots and a great victory of those who understand the word sovereignty and understand the significance of sovereignty."
Praising the new canal, Duda said that "the waterway will allow for free navigation between the Baltic Sea, the Gdansk Bay and the Vistula Lagoon, (and the towns of - PAP) Elblag and Tolkmicko."
Prime Minister Mateusz Morawiecki said at the opening ceremony that the shipping channel is "a way towards freedom, new opportunities and new possibilities" and "a testimony to the will, ability to fulfil, and striving for a strong, independent and sovereign Poland.
"Today, on the 83rd anniversary of the Soviet Union's attack on Poland, in a symbolic way, we are breaking the last ties of our factual... dependence on the Soviet Union, and then on the Russian Federation," he added.
Russia has opposed the canal arguing that it will allow Nato warships to enter the Vistula Lagoon without passing close to Russian military facilities at Baltiysk, and therefore it represents a direct threat to the security of Kaliningrad and the Russian Federation as a whole.
On September 17, 1939, sixteen days after Nazi Germany started World War Two by attacking Poland, Soviet troops invaded the country following a secret agreement with the German Third Reich which called for dividing up Poland's territory between the two totalitarian states.
The 1.3-kilometre canal is part of a massive project which required the construction of 22.8 kilometres of new water routes, an artificial island and civil engineering and road infrastructure. Although navigation is allowed from September 18, the project will continue with two more stages planned that include strengthening of the River Elblag banks and the construction of harbours and a bridge as well as changes to road infrastructure. The waterway is also planned to be deepened in the future. (PAP)