Fish, Wildlife and Parks are investigating why dead fish washed up on the shores of Georgetown Lake over the weekend.
Brad Liermann, FWP fisheries biologist, said Monday that he and other officials will take a boat out onto the lake Wednesday to try to determine the cause. Currently, Liermann said he doesn’t know how many fish have perished nor the species.
But he said the likely cause is low oxygen levels in the lake over the winter.
“The oxygen numbers were really poor going into late winter,” he said.
Because of that, the fish could have run out of oxygen.
The Department of Environmental Quality said Monday that the enforcement division hasn’t received any reports regarding fish perishing and washing ashore at Georgetown Lake.
But Liermann said he’s gotten phone calls from the public.
Liermann said Georgetown Lake is particularly susceptible to low oxygen problems. The lake is shallow with a lot of nutrients.
The nutrients are the source of biological productivity, making the lake good for fishing — the fish grow bigger faster and Georgetown has “a lot more fish in there than other lakes,” Liermann said.
But all those microbes, plants and acquatic insects contribute to low oxygen over the winter when the lake is frozen over.
Liermann said the water levels in Georgetown Lake were really high this year, which makes the dead fish a bit of a surprise. The more water there is, the more oxygen there is in the water.
But southwest Montana had a “long winter,” this past season, with ice coming early on the lake and staying longer than usual, Liermann said. The region also saw really deep snow, which reduced the amount of sunlight that gets to the lake.
“That reduces photosynthesis, which produces oxygen, and that makes things worse,” Liermann said.
Liermann said Georgetown Lake hasn’t been this low in oxygen since the early 1980s.
Another potential reason for the deaths could be spawning. Rainbow trout are spawning right now, which is stressful for fish.
“We might never know (the cause) for sure,” Liermann said.