At routine summer releases on the heavily used class II stretch of river, a 14 year old girl nearly lost her life due to being trapped under water by her paddleboard ankle leash.She was wearing a PFD. She was part of a large group of families/friends using a combination of I think 2 rafts, one paddleboard, and 1 or a few IKs. We had noticed them all having fun together as we were floating in the flat water above the first rapid. We came on the scene while she was already trapped underwater. On the first rapid of the run she apparently fell off the paddleboard – she went on one side of a large rock protruding from the surface, and the paddleboard went down the other side. The force of the water was strong on both sides, and she was trapped face down underwater. We could see the commotion from an upstream eddy and quickly paddled over to give assistance. The body could be seen underwater at this time. Luckily the rock was fairly close to the side of the river, and someone was able to wade upstream to the paddleboard and release it around/above the rock. She then floated free – face down/unconscious. She was quickly recovered by a raft in the party, and miraculously came to with rescue breathing/CPR. I am told that she had a full recovery. At least some in the group were quite experienced – just not enough to avoid an ankle leash on the river…Their experience did allow a rapid rescue – she was probably underwater for less than 1.5 minutes. But she was absolutely stuck, and would not have come free without releasing the SUP.