A mystery stench hung over Dartmouth Thursday, near the King's Wharf development. (CBC)

There was a mysterious smell hanging over downtown Dartmouth Thursday.

People called CBC News concerned about a nasty smell in the area, but Halifax Regional Municipality officials said they didn't know where the stench came from.

"Actually it smelled like dead fish to be truthful," said Heather Ferguson.

Locals had different opinions of what the strange smell permeating through downtown Dartmouth could be.

"I don't know. Maybe one of the sewage treatment plants backed up or something. Maybe?" questioned Paul Lynch.

"We were thinking maybe there was something pulled out of the water. Maybe a barge that had barnacles on it or something and it's rotting in the sun," wondered Carolee Nichols.

"Dead bodies you know, like seals or fish. Well it's not really fish smell, no. I don't know what it is," said Bill Nichols.

The smell for many was nauseating and it's still a mystery.

The Halifax Regional Water Commission said there was nothing wrong with the sewage system but an official suggested a few other potential reasons for the stinky air.

He said it might be that the sewage system simply hasn't been flushed lately and rain could help the smell dissipate.

The commission also suggested the stench could have come from the Coast Guard if buoys are decaying on the shore.

The sewage treatment plant seemed like an obvious culprit, but it was out of the stench's reach.

The smell was localized to the new King's Wharf development area.

For people who walked the harbour trail, it was bothersome.

"You could smell different smells when you walk down here before, but not quite this strong," said Ferguson. "I said I wouldn't want to live down here if they're going to have a smell like that, but I don't know if it's a temporary thing or not."

HRM confirmed it got a lot of complaints Thursday.

The commission sent crews over to put out large deodorant blocks to try to mitigate the smell.

By late Thursday night, the smell was still very strong.