An Ottawa police officer has been charged by Ontario's police watchdog after a man suffered a serious injury following an arrest in May 2018.

The Special Investigations Unit (SIU) said Thursday it's charging Const. Liban Farah, 33, with assault and obstruction of justice.

On May 9, 2018, Farah was patrolling the ByWard Market when he became "involved in an interaction" with a 24-year-old man at about 2 a.m., the SIU said.

The man was arrested and taken to hospital, where he was diagnosed with an unspecified serious injury.

Farah is expected to appear in court Sept. 3.

Charges 'paralyzing,' union head says

The head of the union representing Ottawa police officers was critical of the SIU for taking 15 months to investigate Farah.

Matt Skof, president of the Ottawa Police Association, said he believes police oversight is critical but that taxpayer resources are wasted by an arduous investigative process.

Skof also said Farah is frustrated by the charges laid.

"This is questioning the intent of our profession ... it is very paralyzing on the profession and very difficult for our officers," said Skof.

The SIU investigates deaths, serious injuries and allegations of sexual assault involving police in Ontario.