The appalling incident, on November 7, 2015, only became known of at all because one of the victims bravely decided to go to the police in the aftermath of the Cologne sex attacks.
She told the city's Express newspaper how she and her friend were surrounded by migrants at the party, which was held on a boat, and were repeatedly groped despite asking the men to stop.
She said: "I guess there were about 100 to 150 asylum seeker men there. I'd only been there a few minutes, and I got the first hand on my breast."
Soon the fondling increased even further until there were "up to four men were pressing themselves on me and my friend at the same time", according to the victim.
She said one migrant then grabbed her and kissed her, at which point she managed to break free and run off with another friend.
Once again, the interests of the asylum seekers were placed above those of the German women:
But the council official responsible for integration matters, Coletta Manemann, who helped organise the 'Refugees Welcome' event, did not report the incidents and has now been accused of a cover-up attempt.
Admitting that she knew about the incident "shortly before Christmas" after talking to students who had been assigned to helping the refugees, she said: "I can't remember any more if I told them that they needed to go to the police or not."
Amazingly she said she later concluded that "the student organisers had learned from the situation" and felt there was no need to make a fuss.