The Lane County Sheriff's Office said Spencer was killed in a recreational accident. He was a young man.
Triangle Lake is a popular location for cliff jumping and natural rock waterslides.
"So full of life in every moment of the day," Lanning wrote on his verified account. Spencer, you will be missed. I'm in love with you.
The Lane County Sheriff's Search and Rescue personnel helped bring him back to the road after bystanders and paramedics couldn't resuscitate him.
He was going to start his fifth season at the University of Oregon. He caught 13 passes for 87 yards and a touchdown in 14 games. He had three touchdown catches in the year.
He was the top-ranked tight end in the state.