A pontoon boat carrying the dreaded invasive quagga mussel was intercepted Friday morning at the main boat ramp of McPhee Reservoir.

Colorado Parks and Wildlife invasive-species inspectors stopped the boat before it entered the water.

“It’s proof prevention works,” said Tom Rice, recreation manager for the San Juan National Forest, which helps oversee McPhee.

Lake managers began stricter access protocols this year to prevent contamination by the mussel, which can clog irrigation equipment and cannot be eradicated once in a waterway. Motorized, trailered boats can only access the lake through boat inspection stations at McPhee and House Creek boat ramps during open hours.

The infected boat caught Friday was put on a custodial status by Parks and Wildlife and secured in a yard until it can be fully decontaminated.

Parks and Wildlife spokesman Joe Lewandowski said the owner of the boat has been cooperative. The man told officials he bought the engine on Craig’s List, but became suspicious when he learned it was from Lake Powell, which is infested with the mussel.

This is the third boat this year that has showed up in Southwest Colorado with adult mussels attached. In April, Parks and Wildlife quarantined a houseboat parked on Mancos Hill that had mussels, and another infested boat showed up at Ridgway Reservoir.

“We are surrounded by states positive with the mussel, and preventing them here will take great vigilance from the public and cooperation from boaters,” Lewandowski said.

He warned the public to be wary of boats and engines for sale because many people are trying to dump them because of mussel infestation. Lakes in Utah and Arizona are infected with the mussel, and some prevention regulations depend on boat owners taking action, and that does not always happen, officials warn.

Boaters should always drain, clean and dry boats before and after leaving any waterway. Mussel larvae can survive in standing water for up to 28 days.