A teacher from exclusive Sydney private school Knox Grammar has been charged with possessing child abuse material after a mobile phone was found at the school's aquatic centre.

Key points: Knox's director of aquatic sports was arrested on Monday afternoon

Knox's director of aquatic sports was arrested on Monday afternoon Police say a large number of child abuse images were found on a mobile phone

Police say a large number of child abuse images were found on a mobile phone The school says there's no suggestion the images relate to Knox or swim centre students

Nick Warby, 30, the school's director of aquatic sports, was arrested on Monday afternoon.

Police had searched his home and found six USB drives and allegedly found substances, believed to be ice and GHB, in his car.

Four phones and a laptop were also seized from his home, car and from Knox Grammar.

Mr Warby was charged with possession of child abuse material and drug possession and today appeared in Hornsby Local Court, where his parents watched from the public gallery.

A police prosecutor told the court that the USB drives that were seized contained some files that were "physically obtained" rather than sourced from the internet.

The court was told some of the images fell into "almost the highest" category of offence.

According to Mr Warby's LinkedIn profile, he has been teaching at Knox Grammar since January 2017.

Prior to that he was a primary school teacher. He is also a surf life saver.

Police had opposed bail for Mr Warby, arguing he posed a risk to the community.

Nick Warby was the Knox director of aquatic sports.

However, Mr Warby's lawyer Philip Cox told the court his client had cooperated with police and that he had medical issues.

Mr Cox also argued he had the support of his family.

"He has a safe family home to reside at … he agrees not to have any mobile phone use and will not hold any device," he said.

He said his client would not enter a plea in court on Tuesday as the police facts were a "work in progress".

He was granted bail on the condition he not access the internet, use telephones or approach anyone connected with Knox Grammar.

In a letter to parents, Knox headmaster Scott James said a colleague had discovered "inappropriate images" on a mobile phone.

Mr James said the images were immediately brought to his attention and he informed police.

"They've advised us there is currently no suggestion the images relate to Knox boys or swim centre students," he said.

Mr James reassured parents that the school operated with a "gold standard for the protection of those in our care".

"We will not hesitate to contact police and remove staff who fail to follow our code of conduct and the law," he said.

"The school remains vigilant in its commitment to ensuring we provide a safe supporting environment for our students."

He said it was now a matter for the police and the school would not be commenting further.