NORTH LAWNDALE — As the city comes back to life after a cold, snowy winter, heaps of dead fish have washed up on the shores of the ponds and lagoons in the city’s parks.
In Douglass Park in North Lawndale, the shores of the pond were lined with piles of decaying fish carcasses. Residents were similarly dismayed to see how many fish in the Garfield Park lagoon perished.
“I’ve been a resident of the Garfield Park area for 57 years. I have never seen this many fish dead ever in the lagoon,” a neighbor posted on Facebook.
The combination of the cold streak in February, a mountain of snowfall and a swift warm-up in march contributed to the mass die-off, park district officials said.
The fish died from suffocation caused by tumultuous weather conditions reducing the oxygen supply in the water, officials said.
“If a spring warm-up happens very quickly, as it did this year, the low [dissolved oxygen levels] can cause some of the fish to die-off as they become more active,” said park district spokeswoman Michele Lemons.
The park district typically runs aerators in the lagoons to ensure the water is rich in oxygen through the spring, but the aerators cannot be activated until the ice has fully thawed, Lemons said.
The city’s ponds are a sensitive ecosystem since they are relatively small and shallow, said Austin Happel, a freshwater research biologist at the Shedd Aquarium.
“Being shallow they can be pretty influenced by the air temperature around them. So if it gets really hot or really cold they the water temperature will kind of migrate in that direction at a rapid pace, which can be really stressful for fish,” Happel said.
One common species of fish, the American gizzard shad, is especially sensitive to cold weather, Happel said. Chicago is at the northern edge of the gizzard shad’s range, so too many days with single-digit temperatures can cause them to die.
“They usually have a hard time in winters when it gets really cold,” Happel said.
Extended periods of snow can also cause a “winter fish kill” where many species of fish die suddenly, Happel said. When snow accumulates on a frozen pond, it blocks light from nourishing algae and other aquatic plants.
“It’s completely dark in the system. None of the plants can photosynthesize and create oxygen,” Happel said.
Several blizzards in January and February dropped a whole winter’s worth of snow on the city. Over 40 inches of snow fell within a three-week period, according to the National Weather Service. On average, Chicago gets 36 inches of snow across the entire winter, according to their records.
The massive die-off of fish may be jarring, said Rob Kruml of the Chicago Fishing Club, but it is a natural response to the weather conditions.
“It’s sad to see the fish sitting there. It really is. But fish kills happen every year,” Kruml said.
Similar winter conditions in late 2014 and early 2015 caused a winter fish kill, Happel said. Nearly 20 inches of snow fell on the city in a blizzard that ended early February 2015.
“We had super cold weather and tons of snow,” Happel said. “Those combined to create a bunch of fish kills in the area.”
Just last year, there were also major fish kills in the McKinley Park pond on the southwest side, and at LaSalle Lake in Marsaille, Illinois, said Brian Caunter, a staffer at Henry’s Bait Shop in Bridgeport.
Typically after a die-off, fishing is put on pause for a while to allow the population to recover, and the pond may be restocked with more fish.
“Usually the next year, the fish are a little smaller,” Caunter said.
Pascal Sabino is a Report for America corps member covering Austin, North Lawndale and Garfield Park for Block Club Chicago.
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