During the summer and autumn, the fairways to Västerås and Köping have been dredged with the help of a Danish vessel to enable larger vessels to pass in the fairway.
According to Västerås Tidning, the work was completed last week due to icing.
The damage to the Danish ship's hull indicates that it was hit by the larger British ship, according to the rescue service Syd.
One person has been found dead on board one of the ships.
Another person has disappeared.
An investigation into gross causing of another's death, gross sea drunkenness and gross negligence in maritime traffic has been initiated.
Two people have been arrested.