Around a hundred young people were at the public swimming pool in the town when the 19-year-old and another man dived under a pool cover.
When the 19-year-old failed to resurface, others went to his rescue. They called the emergency services and he was taken to hospital but he could not be resuscitated.
According to Dan Jones at Västerbotten police, it was mostly high school students who were in the enclosed pool area. They had come from various parts of the region but the 19-year-old came from Vännäs itself.
Police said that a crisis centre had been set up to give support and guidance to shocked friends and onlookers.
Another young man was seriously injured in a separate bathing accident, this time near the Edsberg manor house in Sollentuna.
The man, who was said to be in his twenties, was bathing with friends in Edsviken when they noticed that he was floating away from them.
They dragged him up onto land and he told them that he had lost the feeling from his neck downwards. His head was bloody.
The water was not deep in the area and according to a police spokesman he could have injured himself diving in.
The man was taken to Karolinska hospital for treatment.