BOULDER, Colo. (AP) — Environmental groups say plans to expand a Boulder County reservoir would threaten an imperiled species of trout.

The Daily Camera reports the groups filed a 60-day notice that it plans to sue the U.S. government and Denver Water in federal court for alleged violations of the Endangered Species Act if the Gross Reservoir expansion moves forward.

The groups say that filing the expanded reservoir would require greater diversions of water from Colorado River tributaries that are habitat to the green lineage cutthroat trout.

The environmental groups say federal wildlife officials failed to properly analyze the threat to the fish when the project was approved.

Denver Water CEO and manager Jim Lochhead said in a statement the project will benefit the environment by increasing water flows in rivers and streams in Grand County.