A months-long construction project at a major downtown intersection starts this week. Here is what you need to know.

Two TTC streetcar routes will be on diversion for the next four months as work begins on a major construction project at the foot of Bathurst Street.

The City of Toronto is replacing a 105-year-old watermain underneath the intersection of Bathurst Street and Lake Shore Boulevard, with the construction expected to begin on Tuesday.

The TTC, meanwhile, will be simultaneously replacing streetcar tracks in the area.

That work, which begins today, will result in a months-long diversion of both the 511 Bathurst and 509 Harbourfront streetcar routes.

The TTC says that the 511 Bathurst streetcar will be operating from Bathurst Station to King Street West during the closure, with replacement buses operating from Bathurst Street at Queen Street West to Exhibition Loop.

The 509 Harbourfront streetcar will operate from Union Station to Queens Quay West at Spadina Avenue, with replacement buses operating from Queens Quay West at Spadina Avenue to Exhibition Loop.

The TTC says that it expects streetcar track renewal work to be completed sometime in May, with regular service scheduled to resume in late June following further restoration work and testing.

There will not be a full road closure as a result of the work but the city is warning of lane closures and other traffic impacts.

The city says that there will be no southbound travel on Bathurst Street during the second phase of the project, which runs from early March to mid-April.

The city also says that while at least one lane will be kept open in each direction on Lake Shore Boulevard, turning will be prohibited at Bathurst Street.

Construction will be taking place 24/7.