The planned rail line will run 12.5 kilometres from Tunney's Pasture in the west to Blair station in the east, and will include a 3.2 kilometre tunnel under the downtown. (CBC)

Ottawa's light rail transit plan passed another milestone Tuesday when the Ontario Ministry of the Environment approved its environmental assessment.

"Environmental assessments for infrastructure projects of this magnitude are extremely rigorous," said Mayor Larry O'Brien.

"The speed at which our plan received the green light is a testimony to both the quality of our proposal and the hard work of our city staff," he said.

The rail line will run 12.5 kilometres from Tunney's Pasture in the west to Blair station in the east, and will include a 3.2 kilometre tunnel under the downtown.

In June, the federal government announced it would contribute $600 million to the $2.1 billion project.

Last December, the Ontario government said it would contribute $600 million to the project.

The city submitted its environmental project report to the province in June.

The city said the report "examined everything from noise and vibration levels to air and water quality and the preservation of vegetation, wildlife and local heritage sites along the planned route."

Alex Cullen, the chair of the city's transit committee, said the provincial approval shows that the city is on the right track with the LRT plan.