The Colorado Parks and Wildlife Commission voted unanimously Thursday, Nov. 16, to modify fishing regulations at the Dillon Reservoir, Blue River and Tenmile Creek in response to a decline in brown trout.

During the commission’s meeting, Colorado Parks and Wildlife Regulations Manager Hilary Hernandez said the changes require all brown trout over 14 inches in length be returned to the water immediately upon catch.

The regulations also create a seasonal closure to parts of the Blue River and Tenmile Creek from Sept. 1 to Dec. 1, Hernandez said. The commissioners did not discuss the regulations before voting.

Colorado Parks and Wildlife aquatic biologist Jon Ewert said during a discussion in Frisco in May that Colorado Parks and Wildlife proposed the regulations because of a 10-year decline of brown trout over 15 inches long in the Dillon Reservoir.

Though the reservoir was once known as a destination for catching big brown trout, the decline of brown trout over 15 inches in the past 10 years suggested that local regulations to protect the species may be necessary, Ewert said at the time.

“I don’t have the impression that there is a huge amount of harvesting going on out there and that harvest is the culprit,” Ewert said. “But when you’re trying to restore the large fish in a fishery like this, you need to enact something to rule out the possibility that harvest is playing a role.”