Police say a man who jumped into Lake Ontario near Sugar Beach has died.

The man, around 30 years of age was drinking on the beach with a woman when he decided to take off his clothes and go for a swim, according to police.

Within minutes the man began to struggle in the water and the woman called out for help.

Workers at the nearby Redpath Sugar refinery attempted to rescue him by throwing a life preserver. The woman he was with also jumped in the water and tried to save him, but she was unsuccessful.

Police marine unit was conducting tests nearby

The police marine unit was conducting tests nearby and reached the scene in minutes. (CBC/Petar Valkov)

Police and fire were called around 11:30 a.m. and a police marine unit was the first to respond.

"Our marine unit was doing training within the area," said Det. David Wallace. "They were here in about seven minutes, which is extraordinary."

Within minutes of arriving, divers were able to locate the man's body. Wallace said he was underwater for more than ten minutes and had no vital signs.

The man was rushed to St. Michael's hospital in life-threatening condition where he pronounced dead on Monday afternoon.

Toronto police are seen gathering the man's personal items left on the beach. (CBC/Petar Valkov)

The woman was also taken to hospital and is expected recover. Police say she has been co-operating fully with their investigation.

"We are seeking witnesses from around to contact police at 51 division," said Wallace.

Police are also canvassing surveillance video from the area that may shed some more light on what happened.

An autopsy on the man's body is expected to take place in the coming days.