Water tests conducted by Youngstown State University confirmed it was low oxygen levels that resulted in the deaths of hundreds of fish in July at the Lily Pond in Mill Creek Park.
The diluted oxygen levels were caused by a variety of factors, said Kirsten Peetz, natural-resource manager for Mill Creek MetroParks. The first was that weather had been hot, in the upper 80s or low 90s for a week.
“The heat was then followed by a very hard rainstorm that mixed with the pond and further diluted the dissolved oxygen levels,” she said Monday at a park-board meeting. “It was literally a perfect storm of conditions” for the fish kill.
Shallow ponds are more susceptible to reduced oxygen levels from heat, and despite the fact the Lily Pond is fairly large — it covers more than 3 acres — it is no more than 5 feet deep, Peetz said.
Any time the dissolved oxygen levels are below 3 milligrams per liter, fish start to die. The YSU testing showed the pond levels were at 1.8 milligrams per liter, she said.
When asked how a similar incident could be prevented in the future, Peetz said, “We are considering an aeration system that would keep adding oxygen to the pond at all times.”
It would take three aerators to do the job at a cost of $7,000 each, and electricity would have to be run to the pond, she added.
Resident Christine Fleck questioned if some of the brush that had been removed from around the pond had made it easier for the water to warm.
“Possibly with some of the edge areas of the pond, but overall, that does not appear to be a factor,” Peetz answered.
Fleck also questioned if any pesticides used near the pond could have caused the fish to die and if turtles or any other wildlife in the pond were impacted.
“We saw lots of frogs, toads and turtles alive at the pond,” she said. “If it would have been a pesticide, frogs, particularly because they absorb everything through their skin, would have been affected,” Peetz said.
All pesticides that are used at the park are used according to instructions and according to protocols, she added.
Peetz said there were some of each variety of fish in the pond that survived, so the pond’s fish would repopulate naturally.
Park officials did not count the exact number of dead fish that were removed, but they filled six 30-gallon drums, she said.