A leaked report into a surge in sex crimes by immigrants at German public swimming pools is a 'grave concern', according to officials.

The secret report's authenticity has been confirmed by the authorities in Dusseldorf which outlines the particular worry over rapes and sexual abuse of children.

It comes just months after the nightmare scenes in Cologne on New Year's Eve when hundreds of women were sexually abused by marauding gangs of migrants and less than a month since an Iraqi migrant was jailed for raping a 10-year-old boy in an Austrian swimming pool.

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The migrant was jumping from the diving board at Theresienbad pool (pictured above) when police came to arrest him with the man now sentenced to six years jail

Out of control: Footage of New Year's Eve in Cologne shows the celebrations going terribly wrong as police try to control the huge crowds of revellers where hundreds of women were sexually abused

The internal report was issued for officers of the Criminal Commisariat 12 - responsible for sex crimes and missing persons - and states: 'The K12 can confirm a surge in sex crimes at these establishments.

'In particular rape and the sexual abuse of children in bathing establishments have given us grave cause for concern.

'The perpetrators are, for the most part, immigrants.'

The Bild newspaper revealed the document on Monday - just six months after the nightmare scenes in Cologne on New Year's Eve when the German welcome mat for refugees was well and truly rolled up.

In and around the main railway station on December 31 hundreds of women were sexually abused and robbed by marauding gangs of migrants as the police failed to tackle the situation.

Ever since then the number of migrants - men from sexually repressive Muslim countries - attacking scantily clad women and children at swimming baths has continue to soar.

Many cities, including Munich and Berlin, have posted charts in numerous languages stating that women wearing skimpy bathing costumes are not telegraphing that they are available for sex and must not be touched inappropriately in any way.

The memo from the Duesseldorf sex crimes unit comes as the open-air pool season in Germany is in full swing.

It stemmed from a meeting of sex crime officers on June 15 in which the escalating incidents - including two rapes at a swimming pool - were discussed.

The clarification of the cases was 'particularly difficult' because of the numbers of people in the mobs.

Officers vowed to improve their policing methods including more photofits of suspects together with accurate description of their clothing at the time of the attacks.

A police spokesman confirmed the authenticity of the document and said it was a meeting designed to assure the quality of investigative work and that there had been a meeting.

Groups of young men light fireworks into the crowds during the New Year festivities, which police later admitted were out of control

One woman can be heard shouting for someone not to touch her in the background of the video

Last week in Austria a 13-year-old girl said she was attacked by an immigrant man at a public baths.

But she kept changing her story and in the end admitted she made it up.

This was not the case in December last year, when a 10-year-old was raped in an Austrian swimming pool by an Iraqi migrant.

The asylum seeker, who had not had sex for four months, said it was a medical emergency when he raped the boy in a swimming pool changing room.

The 20-year-old, who had been taken to the Austrian swimming pool Theresienbad, pictured, to be taught how to integrate into his now community, was found guilty of serious sexual assault and rape of a minor and was sentenced to six years in jail.

The young victim loved going swimming at the local pool in Vienna but now suffers from severe post-traumatic stress disorder and panic attacks

The man, who had fled to Austria through the Balkan refugee route in September last year, hung his head in shame before he was sentenced for the horrific crime which left his victim suffering post-traumatic stress.

The migrant had been taken to the pool in December 2015 with a 15-year-old helper and translator who was helping him to integrate into life in the Austrian capital Vienna.

But while there, the 20-year-old man dragged a boy, 10, into the change rooms and attacked him.

The boy, known only as Goran, was also the son of an immigrant family from the Balkans who grew up in Austria with his Serbian mother.

The horrific attack was so violent that the young boy needed to be treated at the Children's Hospital, and is now plagued by massive post-traumatic stress disorder.

Goran went to a lifeguard in tears after the attack but the Iraqi involved in the attack was so brazen that he had not even left the swimming pool.

Instead, he was jumping off a three-metre diving board when police arrived to arrest him.

He told police the attack was a sexual emergency as he had not had sex for four months after leaving his wife behind and coming to Austria as an asylum seeker in September 2015.

The pool's lifeguard immediately called police who immediately hand-cuffed the man

Court Psychiatrist Gabriele Woergotter confirmed the 10-year-old victim now suffers frequent panic attacks.

The courts awarded the victim 4,730 EUR (3,750 GBP) compensation.

The man faced up to 15-years in prison under Austrian law - but was given a lower sentence apparently due to his young age, and previous good behaviour.

The court also took into account the man's 'adverse living conditions' when deciding on the sentence.