Methods used to protect cities and farmland from flooding in the province are having an adverse effect on salmon, according to new research.

A report by researchers at Simon Fraser University found that dikes and floodgates can compromise salmon habitats in the Fraser Valley. The study of more than 20 tributaries in the region found that upstream habitats were negatively affected where floodgates remained closed for longer periods.

“The findings of this study highlight an important opportunity to change how we operate floodgates and improve conditions for salmon and other native fish species,” said Rebecca Seifert, the lead author of the study. “Upgrading flood infrastructure is an ongoing discussion in the region and there are opportunities in this planning process to consider impacts to fish.”

Using time-lapse photography, the researchers recorded the amount of time that the floodgates were open at each location and found poorer oxygen levels and biodiversity in the areas where access was more restricted.

The floodgates not only prevented fish including trout, coho, and chum salmon from passing through, but they also cut off the flow of fresh water in the streams. The researchers observed that nearly half of the floodgates in the study were open for less than 20% of the day.

Low oxygen levels in the water can have an effect on the vitality of sensitive fish species like salmon, according to Seifert. The pumps that accompany the floodgates can also pose a lethal risk to some of the fish.

The Fraser Valley is a major source of agricultural production in the province and the regional district reports that nearly half of the area is prone to flooding. There are over 400 floodgates and more than 600 kilometres of dikes used to protect homes and farms from seasonal flooding.

“It is possible for salmon, farms, and cities to co-exist,” said Tanis Gower, a biologist with the Watershed Watch Salmon Society, adding that many salmon species are in trouble and freshwater habitats are one of the few factors that people are able to control.

Gower recommends opening the floodgates for longer periods and using fish-friendly water pumps that won’t grind the fish to improve the habitat in the Fraser Valley.

“People should know that there is a vast amount of salmon habitat that we’ve cut off, and that while it will never be the way it once was, that there is a lot of room for improvement,” Gower said.  

However, another report out of the University of Victoria commissioned by the Watershed Watch Salmon Society suggests that monitoring of the habitats in close proximity to floodgates and dikes is also being neglected.

“No one is effectively overseeing the more than 1,400 km of salmon habitat behind floodgates in the lower Fraser Valley,” said Deborah Curran, a law professor and author of the report, in a press release. “It’s quite startling to see.”

The report suggests that the local, provincial, and federal government all have responsibility to oversee the health of salmon populations that are affected by flood-prevention methods.  

“We are working with all levels of government for change,” added Gower. “This is good timing, as all the flood infrastructure is being studied to determine priorities right now.”

The Fraser Basin Council — a collaboration between government and local organizations — is currently leading a six-year review of flood systems in the Lower Mainland to better protect the area from coastal flooding.