Pellet-fed trout, artificial side channels, and extensive in-stream structures have drawn scrutiny in a new CPW report. (Courtesy of Colorado Parks & Wildlife)
January 05, 2026
By Fly Fisherman Staff
A new Colorado Parks and Wildlife survey of the Blue River near Kremmling documents sharp seasonal swings in trout numbers, heavy gill‑lice infestations in rainbow trout, and signs that private stocking and pellet‑feeding upstream are influencing the fishery. CPW found that in fall 2018, “Brown trout made up 98% of the trout population by biomass,” but spring surveys showed steep declines and a higher proportion of rainbows—many of which carried PIT tags from a private landowner’s stocking program. The agency reported that all rainbows captured were “heavily infected with gill lice parasites,” with infestations among the worst observed in Grand and Summit counties.
These findings echo concerns raised in Fly Fisherman's initial reporting on Blue Valley Ranch –known as “Jurassic Park”–where pellet‑fed trophy trout, artificial side channels, and extensive in‑stream structures have long drawn scrutiny. Guide and shop owner Ben McCormick argued that declining trout numbers have little to do with boat traffic and instead reflect “unnatural occurrences that are happening within the ranch,” including pellet feeding, altered flows, and habitat manipulation. He added, “I’ve seen pellets floating on the river all the way down to the confluence with the Colorado River… Chumming is illegal in Colorado, so how are they allowed to do this?”
CPW highlighted concerns over how the fish feeding can upset the natural biomass of a fishery, pushing resident fish out as the rainbows get larger. It added that angling mortality is likely "minor compared to natural mortality rates, especially in this stretch...".
“Many of the fish that we handled in these surveys also had large amounts of fish feed in their stomachs,” explained the report. “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.”
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A new Colorado Parks and Wildlife survey documented heavy gill-lice infestations in rainbow trout. (Courtesy of Colorado Parks & Wildlife) CPW’s survey also documented the first confirmed presence of mountain whitefish in the Blue River, indicating the non‑native species is expanding its range upstream from the Colorado. Despite disease concerns, artificial feeding, and flow‑related fish movement, CPW emphasized that “the public gained valuable access to a highly unique river reach that hosts a productive fishery.” The agency plans continued monitoring as debates over access, ethics, and river health continue to intensify.
