Heat depleting the oxygen level in Brydon Park Nature Lagoon is being blamed for killing 500-1,000 fish from Aug. 1-4.
Langley City continues to investigate, having samples tested to ensure no chemicals were dumped in the lagoon beside the Nicomekl Flood Plain at about 199th Street and 53rd Avenue.
â€œWe do not stock any fish there,â€ said City administrator Francis Cheung.
The fish found were catfish, shiners and pumpkingseeds, all having been dumped by people or the offspring of fish dumped into the lagoon.
Shiners is a common name for silver-sided fish. None of the found ones are native to local waterbodies.
The pumpkinseedâ€™s natural range in North America is from New Brunswick down the east coast to South Carolina. It then runs inland to the middle of North America.
The City received a call Friday afternoon, Aug. 1 and staff went to the site.
â€œWe found about a dozen fish floating,â€ Cheung said.
Another call came in that evening.
The City contacted the Ministry of Environment, the Langley Environmental Partners Society (LEPS) and the Conservation service.
Water samples were taken for testing and LEPS helped with clean up. The City has asked LEPS to do another water test and is monitoring oxygen levels as well as checking for possible other causes.
The Langley Field Naturalists helped turn the former sewage lagoon into a nature park which has a perimeter trail and benches.
Itâ€™s a site for birds, dragonflies and other animals and insects but not fish. Itâ€™s never been stocked by the City.
â€œWe donâ€™t want to stock any fish in there because itâ€™s so shallow,â€ Cheung said.
The water comes from stormwater runoff of the surrounding neighbourhood and a weir controls the water level.
The sewage lagoon was decommissioned in the 1970s when the City joined the Greater Vancouver Regional District sewage system.
The lagoon had algae blooms in 2006 and 2008, when hot conditions were right for the phenomenon. Any bloom right now is not considered cause of the fish kill. The heat warming the water and causing oxygen levels to drop is the current theory.
The City worked with the Field Naturalists to create a natural lagoon setting, including aerators to keep the water from becoming stagnant.
A pump specialist was called in this week to see why one of the two aerators is faulty.
â€œOne of the pumps has been operating intermittently,â€ Cheung explained.
The lagoon is about one metre deep at its shallow end and about two metres at the other.
There are no plans to alter that. The City had the pond studied a few years back and the cost to dredge it could be in the area of $1.5 million.
Cheung said the cost was considered prohibitive.
He added that there are environmental implications with heavy metals and any other contaminants flushed in decades past and sitting within the sediment at the bottom.
â€œBecause itâ€™s an old sewage lagoon, we may stir up more of an issue,â€ he said.