Lost Lagoon is full of dead fish again. What's going on?

There's a bizarre ecological event happening in Lost Lagoon right now, and not for the first time.

Lost Lagoon was artificially created in the early 1900s when the Stanley Park causeway was built. Formerly a tidal ecosystem, it was made into an isolated body of water for Highway 99. Now the lagoon is now a pond for recreational and aesthetic purposes.

For the last few weeks, Vancouverites have reported seeing a number of dead carp floating on the surface of the lagoon or washed up onshore and the city of Vancouver has confirmed that a similar occurrence happened last September as well.

When the carp started turning up dead in 2021 a water quality test was performed alongside necropsies on several of the fish. A spokesperson for the city told V.I.A "while the receiving lab could not pinpoint an exact cause, Staff believe fish mortality was related to the overall water quality of Lost Lagoon—mainly low dissolved oxygen and high salinity from the adjacent ocean in Coal Harbour."

Originally a conservation technician with the Stanley Park Ecological Society had two theories for the dead carp, one of which had to do with a large amount of rainfall that occurred at the time.

Now that the dead fish appear to be a yearly occurrence. The City says that "the Stanley Park Ecology Society runs a continuing water quality monitoring program for the lagoon that may shed light" on what is happening. Along with the dead fish, members of the public have noticed large amounts of algae and sludge on the surface of the pond.

"Because [the lagoon] is isolated, infilling, and now only approximately a metre deep (with much of the shoreline non-naturalized), it is considered an ecologically poor habitat, vulnerable to sea level rise and other climatic events," says a City spokesperson. "Staff have been aware of the ecological issues and challenges at Lost Lagoon for some time and, over the last few years, have been exploring various feasible solutions to restore the area."

According to the City, the lack of flushing that happens naturally in the Lost Lagoon area is a major contributor to the water quality issues, along with other localized environmental impacts. They are currently working on a Lost Lagoon Reconnection Feasibility Study, which explores a possible long-term reconnection of the lagoon to Coal Harbour. The study also connects to the work being done with the Musqueam, Squamish and Tsleil-Waututh Nations as part of the Stanley Park Comprehensive Planning project.

"In the interim, we are developing a sediment handling strategy for sludge that has accumulated over the years at the bottom of the lagoon. Understanding its composition will be essential to informing the remediation options available," says the spokesperson.

With files from Cameron Thomson