The Bellingham Herald reports the swimmer jumped off the lower of two waterfalls at Whatcom Falls Park and did not surface around 8:45 p.m. Monday. A city parks employee nearby jumped in the water to look for him.
Moments later, the swimmer's body was pulled out and first responders performed CPR. He was pronounced dead at St. Joseph's Hospital.
The swimmer has not been identified, although it's believed he was a teenager.
The rescue effort began about 10 minutes after sunset.