Water managers and state wildlife officials last year hoped the discovery of a microscopic zebra mussel larva in the Colorado River was a one-time event, not a sign of a larger problem lurking beneath the surface.

Zebra mussels are similar to another invasive mollusk, the quagga mussel, which has not been detected in Colorado’s lakes and streams. However, they are routinely intercepted on watercraft through the state’s watercraft inspection and decontamination program.