Toronto Mayor John Tory says half of the structures on Toronto Island are threatened by water in the wake of record-high lake levels.

Tory has invited the media to join him and will address them at about 8 a.m., officials say.

The Island was made off-limits to tourists on Tuesday, with only residents and city crews allowed aboard remaining ferries.

Officials estimate that approximately 40 per cent of the park area of Toronto Island is under water. More than 50 per cent of the buildings on the island are at risk of flooding.

"You can see just by walking along here the amount of damage that has been done," Tory told reporters Friday.

Pumps are offloading 500,000 litres of water from the island each hour to help water levels recede.

"We can't have people walking around even in places that appear to be dry," Tory said.

On Wednesday, the Toronto District School Board decided to relocate students at the Island Public School to Nelson Mandela Park Public School in Trefann Court on the mainland.

The City has warned the Island may not open to the public possibly until the end of July as time will be needed to allow water levels to recede to acceptable levels.

Staff says water is receding at a slow pace, about one to three centimetres per week.