Alberta Premier Rachel Notley says concerns about environmental contamination will delay the return of up to 2,000 evacuees hoping to move back to their homes in fire-damaged Canadian oil sands city of Fort McMurray until as late as September.

Notley said Monday that more than 500 homes and about a dozen apartment complexes that escaped a massive wildfire earlier this month in three otherwise heavily damaged neighborhoods are not safe to be lived in yet following tests on air, soil, ash and water. Notley says it's not safe to return until toxic ash and debris surrounding the homes have been removed.

Officials hope to start a phased in return of more than 80,000 evacuees to Fort McMurray starting Wednesday. The massive wildfire destroyed about 2,400 structures in Fort McMurray but 90 percent of the city remains intact.