Montana wildlife officials are investigating what’s being described as a "significant" fish kill along the banks of the Upper Clark Fork River.
Montana Fish, Wildlife and Parks fisheries biologist Nathan Cook fielded a report this weekend of several dead fish downstream of Warm Springs and upstream of Galen.
"It took a little bit of looking, but within the first 100 yards we found some dead whitefish. Then we started to see some dead trout and a dead sucker. Those are the three most common species that we find up in that part of the river. It was alarming."
Cook uses the word "significant" to describe the fish kill.
"Any fish kill where we observe more than just a couple, I would call significant because it’s likely a big part of the population. There just weren’t many to begin with," he says.
Cook saw some 32 dead fish in various states of decay along the riverbanks between Galen Road and Perkins Lane; an area still contaminated with high levels of pollution left over from decades of old mining operations.
"I suspect we only saw a fraction of the fish that were originally killed by whatever event got them."
That’s because birds were feasting on the carcasses. Cook suspects many other dead and dying fish sunk or were swept downstream.
There’s no definitive explanation yet, but he has a working hypothesis.
"Starting about Friday this part of the world has gotten a lot of rain. Those fish kills that have happened in the past, a lot of times they were shortly after big rain events. Rain starts to run overland and It’ll pick up a lot of metals from those contaminated areas that we call slickens. Those metals can get into the river."
Slickens are pieces of ground in the upper Clark Fork watershed devoid of life due to heavy metal contamination dating back to an early 20th century flood that washed mine waste off of the Butte Hill and down river all the way to Missoula.
Cook says there hasn’t been a significant fish kill on that part of the upper Clark Fork since the late '80 or early '90.