<P> In the 19th century, the Danube was an important waterway but was, as The Times of London put it, "annually swept by ice that will lift a large ship out of the water or cut her in two as if she were a carrot ." </P> <P> Today, as "Corridor VII" of the European Union, the Danube is an important transport route . Since the opening of the Rhine--Main--Danube Canal, the river connects the Port of Rotterdam and the industrial centres of Western Europe with the Black Sea and, also, through the Danube--Black Sea Canal, with the Port of Constanța . </P> <P> The waterway is designed for large - scale inland vessels (110 × 11.45 m) but it can carry much larger vessels on most of its course . The Danube has been partly canalized in Germany (5 locks) and Austria (10 locks). Proposals to build a number of new locks to improve navigation have not progressed, due in part to environmental concerns . </P> <P> Downstream from the Freudenau locks in Vienna, canalization of the Danube was limited to the Gabčíkovo dam and locks near Bratislava and the two double Iron Gate locks in the border stretch of the Danube between Serbia and Romania . These locks have larger dimensions . Downstream of the Iron Gate, the river is free flowing all the way to the Black Sea, a distance of more than 860 kilometres (530 mi). </P>

Why are there locks on the danube river
find me the text answering this question