… [F]or wetland biologists and others with a stake in the health of the surrounding Sacramento-San Joaquin Delta, the largest estuary on the West Coast, the birds represent the latest – and an exponentially growing – threat to the few remaining wetlands left in California. … Mute swans also feed gluttonously on submerged vegetation, destroying the plant life on which other native wetland species depend. … A measure before the state Legislature aims to allow hunters and landowners to shoot the swans for the next five years to try to bring their numbers down to more manageable levels in the Sacramento-San Joaquin Delta and beyond. 

Other invasive and non-native species news:

• E&E News by Politico: Zebra mussel infestation grows in the Colorado River Basin​
• Vail Daily (Colo.): Eagle River Coalition: Threat of zebra mussels can’t be understated​
• ABC7 (Denver, Colo.): Section of western Rocky Mountain National Park to close for project to remove non-native fish