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At least 16 motorcycle collisions were reported to authorities Sunday during or after the 27th annual Oyster Run, including one fatality on Interstate 5 north of the Skagit County line and four serious crashes in other locations, authorities confirmed today.

A 48-year-old Lynden man died just before 5 p.m. Sunday on northbound I-5 when his bike hit a guardrail, a State Patrol trooper said. His name, Steven Vail, was released today.

Vail’s passenger, a 29-year-old woman from Belfair, was taken to St. Joseph’s Hospital in Bellingham for treatment. Details weren’t available at press time.

Until late Sunday afternoon, few problems were reported to law enforcement.

“We were hoping we were going to get away unscathed,” State Patrol spokesman Trooper Keith Leary said.

Troopers and State Department of Transportation officials had electronic reader boards out warning motorcyclists to ride safe and “share the road.”

The annual motorcycle run, which attracts bikers from all over the Northwest to Anacortes, drew a crowd of 15,000 to 20,000, said Anacortes Police Capt. John Small.

“More people than ever,” Small said. “More bikes than ever.”

As thousands of bikers left Anacortes, traffic gridlocked for 35 blocks in the city, Small said.

Starting about 3:30 p.m. reports began to come in, including three collisions within a half hour of each other, said Chief Tom Molitor, who supervises the Skagit County Sheriff’s Office patrol division.

Most were minor, often involving one bike, deputies and troopers said. Two motorcycles riding next to each other locked handlebars and crashed near La Conner. In separate incidents, at least two motorcycles crashed on Highway 20 near Higgins Airport Road. The causes of most crashes were still under investigation Sunday night.

Reported injures in crashes on Anacortes and Skagit county roads, on Highways 20 and 9, and on I-5 ranged from a sprained ankle to a serious head wound that prompted emergency workers to fly a 44-year-old Bellingham man to Harborview Medical Center in Seattle. He remained there this morning in serious condition, a hospital spokeswoman said.

In the evening, freeway entrances and roads along Highway 20 and I-5 were backed up, and many biker-friendly establishments, such as the Conway Tavern, were packed, Leary said.

Throughout the Oyster Run, troopers and deputies at various spots on highways watched for speeders and other problems. At least 20 officers from Mount Vernon, Oak Harbor, Swinomish and Sedro-Woolley police departments and Skagit and Whatcom counties sheriff’s offices worked the roads affected by the run. Anacortes officers patrolled the city. And troopers patrolled the highways from Whatcom to King County.

Still, when the eye of the law was elsewhere, a few motorcyclists performed stunts on the highway, including one rider who popped a wheelie as he rode west over the bridge at the Swinomish Channel, heading toward Anacortes.

Such antics on the highway are frowned upon by the State Patrol. Troopers had a zero-tolerance approach to motorcyclists breaking traffic laws, Leary said.

A Granite Falls motorcyclist riding near a group of bikers doing stunts lost control of his bike while riding north on I-5 near Stanwood, troopers said. He and his passenger were seriously injured when his motorcycle slid into another bike and they were thrown from the bike. The other driver reported no injury, troopers said.

The injured driver who crashed was following too close, Leary said. His and his passenger’s conditions weren’t available at press time.

Also, a Seattle man was injured Saturday when his motorcycle collided with a brick wall of the Bow Post Office at the corner of Chuckanut Drive and Bow Hill Road remained hospitalized this morning. Clarence Reynolds remained in serious condition at Harborview, a hospital spokeswoman said.

• Marta Murvosh can be reached at 360-416-2149 or .