She calls it "guano."

But she's flexible on terminology.

"You can call it duck poo if you want," says Heidi Boutilier, the municipality's horticulture supervisor for Halifax's Public Gardens.

Whatever you want to call the layers of slimy sludge on the bottom of the historic garden's pond, there's an awful lot of it.

Maybe even more than a metre of it.

"It's not like we've gone in there and measured it, but it could be between two and four feet," Boutilier said.

A likely contributor to the organic material at the bottom of the pond in Halifax's Public Gardens. (Paul Poirier/CBC)

Pond now stagnant

For decades, the ducks that frequent the Public Gardens have freely released their excrement into the murky waters of what's known as Griffin's Pond. The trouble, is, the feces have nowhere to go but down.

Years ago, Boutilier says, the pond was fed by a freshwater brook, so the current carried some of the organic material elsewhere. But as development encroached, the source of fresh water was cut off and the pond became stagnant.

The thick layer of organic material on the bottom of the pond contributes to the murky, green appearance of the water. (Paul Poirier/CBC)

"Over the past however many decades — or I don't even know how far back it goes, to be honest with you — it has been slowly infilling with organic material. So, leaf litter, duck poop or waterfowl feces," Boutilier says.

The problem was exacerbated by residents and visitors who fed the ducks, which encouraged more birds to hang around. In 2009, the city stepped in to make it illegal to feed ducks in the Public Gardens and other municipal bodies of water.

Cleanup planned

The buildup of organic matter has reached a point where the city has decided to step in — although not literally — to clean it up.

This winter, the municipality will hire a contractor to excavate the pond all the way down to the gravel at the bottom and remove the guano and other organic matter. Boutilier said there's not a set timeline for the work, but it will be done after the ground freezes to minimize damage to the turf and vegetation surrounding the pond.

"This is going to be a big job with excavation and dump trucks," Boutilier said.

Parts of Griffin's Pond are still free of bulrushes and lily pads, but other sections have been overtaken by the plants. (Paul Poirier/CBC)

Municipal spokesperson Brendan Elliott said he can't divulge an estimated cost for the project, as the work will have to be tendered.

"We won't know how much it will cost until we get responses to the tender," he wrote in an email.

"To ensure we are being responsible with tax dollars, we won't be publicly disclosing budget estimates because that might unfairly skew the subsequent bids."

Complaints received

Boutilier says the cleanup should minimize regrowth of algae, bulrushes and lily pads, which are encouraged by the organic matter and have prompted complaints from some users of the Public Gardens. The municipality will also restart a filtration system that has not recently been in use due to the amount of sediment.

Boutilier has not received any complaints about smells emanating from the pond, although the contractors who do the excavation may notice a certain aroma when they do the work.

"I don't think that it's going to create like this perfume in the air unless you're directly around it," she said. "It'll probably smell like rotting organic matter. But it shouldn't be too bad."