Transport Minister Chris Steel said the government did not think the heritage listing would stop light rail being extended across the lake.

"It will add, certainly, an extra layer that we'll need to work through as part of stage 2B in particular, but we were already working on the heritage response," Mr Steel told ABC radio on Tuesday.

Mr Steel said the government's intention to add a third bridge for transport between the two existing carriageways of Commonwealth Avenue Bridge would keep with its heritage values.

The Transport Minister said the bridge had originally been designed for a third bridge down the middle.

"But we need to make sure that as we design the project that we're really respectful of those heritage values and that's already a requirement," he said.

An ACT government spokeswoman said the territory was seeking absolute clarity from the Commonwealth on what impact the heritage listing would have on future infrastructure projects.

"At face value, there appears to be no planning or infrastructure impact for the ACT because the listing covers commonwealth assets and designated land only," the spokeswoman said.

"It has been understood throughout the process that any potential heritage listing would have no significant impact on proposed or future ACT government infrastructure projects."

The spokeswoman said the government would continue to work with the Commonwealth as it prepared the environmental impact statement for the Commonwealth Park to Woden stage of light rail.

Federal Environment Minister Sussan Ley added Lake Burley Griffin and its surrounds to the national heritage list on April 8, the last business day before the election was called.

Ms Ley also rejected a nomination for the city of Canberra, citing a lack of formal position from the ACT government as a reason to knock back the advice of the Australian Heritage Council, which recommended the city's listing.

The Lake Burley Griffin heritage listing is focused more on the values of the area than physical characteristics, and does not prevent changes in the area.

The citation said Commonwealth and Kings Avenue bridges demonstrated significant historic and rarity values of the area,

"Lake Burley Griffin also demonstrates a high degree of technical achievement in engineering. The construction of the two bridges and Scrivener Dam were projects which demonstrated high levels of achievement in their time," the citation said.

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The ACT government spokeswoman said a heritage report commissioned by the government found the original intention of the Commonwealth Avenue bridge was to have space between two bridges reserved for future "mass transport needs", including light rail.

The bridge was designed in 1959 and completed in 1963. Lake Burley Griffin filled in 1964.

"Light rail on Commonwealth Avenue, Commonwealth Avenue Bridge, and through the Parliamentary Triangle has always been part of the original Griffin Plan for Canberra," the spokeswoman said.

National Capital Authority chief executive Sally Barnes in May 2019 said it would be "silly not to look" at the option of a new bridge as part of the light rail works.

"It could be that you start to do that work and it [a new bridge] is either too expensive, or you think 'No, I don't want to get rid of those two bridges because they are quite magnificent'," Ms Barnes said.

"But it would also seem remiss not to at least ask questions."

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