Update 12/20 9:07 a.m.: This story was updated to include comments from Denver Water.
A handful of environmental groups have filed a lawsuit to halt construction on an expansion of Gross Dam in the Boulder County foothills.
Denver Water is proposing to increase the dam’s height by more than 130 feet to store more water from the Colorado River’s headwaters in the reservoir. The suit filed in Denver’s U.S. District Court alleges the construction project would negatively affect the Colorado River, harming native, endangered fish. The suit also argues the proposal runs afoul of the Clean Water Act.