Fish 'die-off' in Stanley Park's Lost Lagoon under investigation

Vancouver -

A number of dead fish have been spotted in Lost Lagoon in Vancouver's Stanley Park over the past couple of days, prompting an investigation by the Stanley Park Ecology Society.

Conservation technician Olga Lansdorp told CTV News they first heard about the fish on Saturday.

“As far as I know, it’s the common carp that is affected by this die-off,” she said, and guessed the number affected would likely be in the dozens. “My first impression is that they look like lethargic fish. It looks like they don’t really have a lot of fight left in them.”

Images and video sent to CTV News by people in the park showed fish floating on the surface of the water in various areas. The society also shared video showing fish clustered together just below the lagoon’s surface.

Lansdorp said while it’s still mystery as to what exactly happened, some possible theories may involve last Friday’s heavy rain.

“There was about 51 millimetres of rain on Friday last week, which is a significant rainfall for September in one day,” she said.

Lansdorp said in late summer, debris that breaks down at the bottoms of ponds lead to a decrease in oxygen levels.

“With heavy rain, everything gets mixed up, and so that low oxygen water gets mixed into the rest of the body of water, and what you find is that there’s a certain tolerance that fish have for levels of oxygen,” she said. “There’s also known to be heavy metals in the sediment at the bottom of Lost Lagoon, so the heavy rain might have stirred up the heavy metals.”

The heavy metals would be a concern, because that could end up travelling up the food chain.

“It’s not just the fish that are using the body of water, it’s also lots of freshwater invertebrates which are then in turn being eaten by birds, which are being eaten by predatory birds,” she said. “I have seen otters eating carp and I have also heard of eagles catching carp.”

Lansdorp said the society is testing the water quality, and will be looking to whether there are any other cases like this in the lagoon’s history, or elsewhere.

She also pointed out the carp are actually an invasive fish, and aren’t native to the area.

“Lost lagoon actually used to be a tidal mud flat, and with the construction of the causeway in the early 1900s, in about 1916, that portion was blocked off and it became a fresh water body of water,” she said. “Ecologically, it’s a type of novel ecosystem.”