The six pairs of Royal Swans were released onto the shores of the Rideau River Thursday, and this summer the city says it won't stand in the way should some of the younger pairs breed.

In the past, the city has had to destroy eggs to control their numbers, said Christine Hartig, the city manager and Honorary Keeper of the Royal Swans.

"Over the years we've had to reduce the numbers by removing eggs because there are just too many to look after," said Hartig.

Queen Elizabeth gave Ottawa 12 birds to celebrate Canada's Centennial in 1967. The last original swan died in 2004.

But over the last 45 years the city has had to, at times, take steps to keep the herd population in check, though the population has soared to 30 at one time.

River, winter facility supports about 12 swans 

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The Royal Swans were released into the Rideau River on Thursday. (CBC)

"There's only so many the river will support and the winter facility supports, so [we] try and stay within those numbers," Hartig said. The facility can support up to 20 swans.

But with an aging flock and a couple of younger pairs coming into breeding age, nature will be allowed to take its course this year, she said.

The city hopes to partner with a private firm to help build a new winter home for the swans to replace an aging facility.