Sherman Reservoir is in central Nebraska near Loup City.
Joshua Rowley, 12, died at the scene after the collision Sunday. The other victim, a 19-year old man, died Tuesday. His name has not been released. Both victims were from Kernersville, North Carolina.
The driver of the pontoon boat, 39-year old Brian Packer of Wood River, was arrested on suspicion of boating under the influence. The results of his blood test were still pending.