The seagulls had a major feast on dead fish at Sego Prarie Pond last week when hundreds of fish died over the June 8-9 weekend.
Bill London, District Conservation Officer for the Idaho Department of Fish & Game responded on Sunday to a report of a large fish die-off at the pond. He found multiple species dead in the water. We visited the pond Monday and saw catfish, trout, perch and even some juvenile frogs who had not lost their gills.
“It’s a pretty rare thing to see all species die at the same time,” said Regional Biologist Art Butts from IDFG.
“When water warms up you will have oxygen depletion causing a kill but usually certain species will die off first,” he said.
It has been determined that what happened was the opposite. The water had become supersaturated with gas from water pumped in to the pond from a city irrigation well.
“Basically the fish got the bends,” said Phil Mamer, supervisor for the Eagle Fish Health Laboratory.
The water, supersaturated with gas, did not allow the fish to breath as the microscopic bubbles filled up the gills and blood.
Toxicology reports show no chemicals were involved and fish are safe to eat although it is unknown exactly how many fish are left in the pond.
Idaho Fish & Game just stocked the pond for free fishing day on Saturday, June 8 prior to the kill but they do not stock urban ponds during the summer due to heat. They have no plans to restock the pond until at least the fall.
Gordon Law, Kuna City Engineer, said that the primary purpose of the pond is irrigation and to his knowledge this might be the first time the pond had been filled with city well water.
“Two and a half years ago the city worked with Idaho Fish & Game to stock the pond and make it a nice park,” said Law. “But the primary purpose is for irrigation. Until the end of June we’ll be putting well water directly in to the pressurized irrigation system. When the weather gets hotter we may have to put well water directly in to the pond again during this low water year.”
This, he said, may cause another fish kill as there is currently no plans to solve the supersaturated gas issue.”
“You can drink water from the well,” said Phil Mamer. “But it’s deadly for fish.”
He said that sometimes when you fill a glass of water and it looks milky, you can look closer and see all the tiny air bubbles in the water. If you let the water sit a while those bubbles dissipate. That’s water supersaturated with gas.
“It will take a while for the saturated gas to dissipate because there is not much stirring going on in the pond,” said Mamer. “They use a degassing column for water at hatcheries but there isn’t one in the pond.”
“We were told it’s the highest reading of supersaturated gas that they had ever measured in pond water,” said Gordon Law.