Biologists Report Trouble For Trout In Blue River

Colorado’s Blue River is back in the news, this time with scientific data to accentuate the challenges trout are facing within the stretch of river near Kremmling. Colorado Parks & Wildlife (CPW) recently completed trout sampling efforts within the Jurassic Park stretch of the Blue, which flows through the Blue Valley Ranch. Ranch owners have long fed and stocked huge trout in the section of river that flows through their land, in addition to building new structures designed to create optimal habitat for jumbo trout.

The issues those manmade alterations to the Blue present anglers are well-documented here, but of particular note to anglers is the CPW data on falling trout populations and overall health problems affecting trout.

The CPW report says that, in the fall of 2018, brown trout comprised 98% of the river’s biomass. By spring of 2023, brown trout only made up 55% of the biomass, with rainbow trout responsible for the other 45%. More alarming is that “all Rainbow Trout captured in these surveys were heavily infected with gill lice parasites,” according to the report.

The report also details how many of the fish caught had fish pellets in their stomachs, and showed signs of heavily relying on artificial food.

“The apparent association between fed fish and heavy gill lice infestation on this reach is a  major concern regarding the health of this fishery as well as the Colorado River in Grand County. Fish feeding has the potential to negatively affect both the brown trout and rainbow trout populations by overcrowding and spreading disease.”

Too many trout concentrated in a river that can’t support that many fish naturally will spread disease and cause problems for a fishery. CPW reports that gill lice are a “highly visible indicator of conditions that have the potential to foster and proliferate other parasites or communicable diseases which may not be as obvious or detectable.”

These disease-riddled fish also have easy access to the Gold Medal reaches of the Colorado River, which adds further concern for CPW.

CPW also commented that there is a 1,600 foot stretch of the Blue they observed that has the qualities of a giant spring creek. They recommend no habitat work on this stretch to help preserve the unique qualities of that piece of water.