For the second year in a row, dozens of dead fish have washed up on the shores of Stanley Park's Lost Lagoon.
The Vancouver Park Board and Stanley Park Ecology Society are still studying the cause of the die-off, but say it's likely because of poor water quality in the shallow lagoon.
"It's pretty dramatic to walk across … because they're quite large, these carp," said Marisa Bischoff, a conservation technician with the Stanley Park Ecology Society.
Carp are an invasive species, meaning they're not native to B.C. and have the potential to harm their environment, but that doesn't diminish the concern surrounding the recent deaths.
Situation similar to last year
Last September, several carp were found floating and washed up on the lagoon's shoreline. Water quality testing was performed alongside necropsies on the dead fish.
The tests did not pinpoint an exact cause for the deaths but the Vancouver Park Board said "overall water quality" in the lagoon appeared to be the culprit.
Low oxygen levels and high salinity from nearby Coal Harbour are largely to blame, the park board said in a statement.
"If the amount of oxygen dissolved in the water is too low for a certain species … then it kind of reduces their biological function at some point," Bischoff said.
Carp, a freshwater fish native to Central Asia, also may not tolerate the high salinity in the lagoon, which has a high concentration of salt in the water due to its proximity to the ocean.
The Stanley Park Ecology Society runs a continuing water quality monitoring program for the lagoon that may shed light on what is shaping up to be a yearly occurrence, the park board said.
Lost Lagoon a 'poor habitat'
The park board says the isolated lagoon, which is about a metre deep, is considered an ecologically poor habitat, vulnerable to sea-level rise and other climatic events.
"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," the park board said.
The pond was originally a tidal mud flat and only became a freshwater lagoon built for recreation and esthetic purposes when the Stanley Park causeway was built in 1938.
Long-term plans in the works
However, solutions are in the works to restore and improve conditions in the lagoon.
Staff are currently working on a study that explores the possibility of creating a long-term reconnection to tidal Coal Harbour.
By reconnecting to Coal Harbour it would become a tidal habitat again and "reintroduce some of that natural ecosystem, natural processes that had been there," said Bischoff.
But she says it would be a very complicated and long-term project.
The study is being done alongside Stanley Park planning work with the Musqueam, Squamish and Tsleil-Waututh Nations to address the challenges in Stanley Park and make improvements.
The park board says it's also 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," the park board said.