What was the Danube Canal built in Vienna for?

The Danube is the second longest river in Europe after the Volga River. Originated in the eastern slope of Heilin Mountain in southwest Germany, it flows from west to east through Austria, Slovakia, Hungary, Croatia, Serbia, Bulgaria, Romania and Ukraine, and flows into the Black Sea in south-central Ukraine. It flows through 9 countries and is the largest river in the world. The tributaries reach Switzerland, Poland, Italy, Bosnia and Herzegovina, Czech Republic, Slovenia and Moldova, and finally flow into the Black Sea in Sulina, eastern Romania, with a total length of 2,850 kilometers (1.770 miles), a drainage area of 8 1.7 million square kilometers, an average annual discharge of 6,430 cubic meters per second and an average annual runoff of 203 billion cubic meters. The Danube has played an extremely important role in the settlement, migration and political changes in Central and Southeast Europe. The castles and forts arranged on both sides of it form the dividing line between the great empires; However, its waterway is a commercial channel between countries.