"Treatments for colds, respiratory infections, and pneumonia include warmth, antibiotics (oral or injected), steaming (with or without medication), breathing oxygen (if the turtle has water in its lungs and cannot get enough oxygen), and X-rays, to check for water in the lungs. "
"Gaping and Yawning:
Gaping can be either totally harmless--turtles do yawn, or a sign of a serious respiratory problem, including pneumonia. You have to watch the turtle carefully and put all the different signs together. If the animal gapes and yawns frequently, and if there are any other symptoms, like swollen eyes, a runny nose, rasping while breathing, or loss of appetite, have a veterinarian evaluate the turtle immediately.
Often a veterinarian will do an X-Ray to determine whether a gaping turtle has pneumonia and water in its lungs. If a water turtle swims lop-sided, mention it to your veterinarian. This is a pretty sure sign, that the turtle does have water in its lungs. "
http://happyturtle.ms11.net/medical.html
what you can dois just keep him warm .. i never heard about this steaming thing..but maybe you should look into it.