Authorities came to the conclusion after comparing crime statistics between 2013 and 2016.
Police have said that “on occasion crimes have been registered in which the perpetrators have have acted from within larger groups,” Die Welt reported on Friday
These type of crime is “notable” because sexual crimes are usually "almost exclusively” committed by people acting alone.
In all the instances of crimes carried out by groups - what the police describe as "a new form of criminality" - the perpetrators were not German, police say.
The statistics also show that in the second quarter of 2016, no more group sexual assaults at swimming pools were registered in Lower Saxony.
Police believe this is due to members of the public being more prepared to report sexual assault in the wake of mass assaults over New Year in Cologne and swifter reaction from police officers.
Whereas around 50 sexual crimes were recorded at swimming pools in the northern state in the previous year, after six months of 2016 “the number is already more than half the average for previous years".
So far in 2016 “a majority of suspects were non-German” whereas in previous years “a clear majority were German", police said.
103 sex crime at pools in NRW