If you dream of this authority doing a strange act, like driving a motorbike into a canal, the implicated meaning is that you shouldn’t trust this authority. This might be a fraud; a fake person masquerading as a person in power. The strange action of wasting a motorbike might be to get rid of it because it is evidence for something that has to be hidden away.

A person of authority is expected to behave honorably with responsibility. So when there is contrary behavior, it looks fishy. You would start to question the sincerity of this person who drove the motorcycle into the canal.