(CNN) -- A deadly shootout in a Washington state park Saturday night was the result of a fight between party-goers attending two separate gatherings at the park, police said Sunday.
Two people were killed and four others were wounded in the shootings at Lake Sammamish State Park in Issaquah, authorities said.
"I think it's safe to say [there was] some gang affiliation in both groups," Sgt. John Urquhart of the King County Sheriff's Department told CNN affiliate KOMO on Sunday.
One group was picnicking at the park, while another was celebrating a birthday, authorities said. Urquhart said a fight broke out between the two groups and someone fired a gun into the air.
"Then there were lots of guns and lots of gunfire," he said.
Police said several guns were found at the scene. Authorities scouring the area where the shootings occurred recovered at least 20 spent casings Sunday, Urquhart said.
"It's unbelievable. It boggles the mind how dangerous this was," Urquhart said, adding authorities are "amazed that more people weren't hurt."