As It Happens

Wildfire causes 80% fish loss in Colorado river, survey finds

The fish in Colorado’s Animas River river have depleted about 80 per cent since last year due to the aftermath of a major wildfire, a new survey of the area has found.

The June 2018 haze brought toxic ash down on waterways, suffocating fish

In this photo taken Wednesday, June 6, 2018, the 416 Fire burns down Hermosa Cliffs above U.S. Highway 550 on the southeast side of the fire near Hermosa, Colo. (Jerry McBride/Durango Herald/The Associated Press)
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The fish in Colorado's Animas River river have depleted about 80 per cent since last year due to the aftermath of a major wildfire, a new survey of the area has found.

Toxic ash from the June 2018 blaze came down on waterways such as the Animas River and suffocated oxygen supply for the fish.

"You've got this floating black ash and debris and chunks of charcoal … to add insult to injury, so to speak," Jim White, Colorado Parks and Wildlife aquatic biologist, told As it Happens host Carol Off. 

The ash spread was aggravated by the subsequent monsoon season from July to September 2018, which caused heavy rainfall and flooding, he said. 

While wildfires are common in Colorado, the 416 fire that raged through southwestern Colorado in June 2018 swept through approximately 219 square kilometres of mainly U.S. Forest Service land in the Hermosa Creek watershed, which include tributaries such as the Animas River, north of Durango.

Oxygen not able to reach fish

White describes the river as having looked like a campfire after water is dumped on it.

"We were obviously in a historic drought down here, so the river flows were very low. And so this ash and debris and solution was not diluted much by other tributaries."

Not only did many fish die, he said, but their size and distribution were also greatly affected. 

A bluehead sucker, a fish native to the Colorado area. Jim White says their numbers are bouncing back better than expected after wildfires in the area decimated the local fish population. (Submitted by Jim White)

There has been a 95 per cent decline in fish longer than 36 centimetres — the historical average size, he said. And fewer fish populate parts of the river that saw greater ashfall.

"These older fish did not handle the change in water quality well at all. They had a pretty devastating fish kill, with fish swimming up on the shorelines and trying to get oxygen," White said. "It was just a mess."

In this Tuesday, June 12, 2018, photograph, hot spots glow after sunset near the Falls Creek Subdivision as the 416 Fire burns near Durango, Colo. (Jerry McBride/The Durango Herald/The Associated Press)

Some fish, such as rainbow and brown trout, are usually raised in a local hatchery and restocked by Colorado Parks and Wildlife. 

However, mottled sculpin, native fish that live on the bottom of the river and are an indicator species of the river's health, were one of the most affected fish species and "may take a little bit longer" to repopulate, White said.

Fish starting to return

Things are not all bad for the river. One native fish, a migratory species known as the bluehead sucker, is repopulating better than expected. 

"These guys have come back and they're actually more abundant than what we've seen in the past, including young fish and juvenile fish, which is a good sign," White said. 

There was also a record snowfall in the area last winter, which White says helped clean some of the leftover sediment.

Fishing in the Animas River, which has Gold Medal status, is a major part of local tourism.

"The electrofishing photos show myself guiding the raft by walking it down the channel, my temporary Pete Deren throwing an electrified "anode" to stun the fish, and retired Sr. Biologist Mike Japhet getting ready to net any fish that are stunned." - Jim White (Submitted by Jim White)

"Part of what makes Durango so special is having a river running right through the middle of town that has this quality gold medal status attached to it," White said. 

"So that's a tough pill to swallow, to lose that angling opportunity for a couple years."


Written by Chelsey Gould with files from The Associated Press. Produced by Morgan Passi.

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