Help needed to reduce ODOR

Question
We have a 15 month large labrador and live on the shores of a small fresh water lake. Last summer he frequently swam in the lake (75 degree water temp in summer and 50 degree in Autumn)
After a few weeks he began producing an odor on the top of his back between shoulders and base of tail. This odor is similar to but not as strong as the anal gland or fear gland emmissions one experiences a few times each year. As soon as he reduces swimming to once a week or less, there is no smell at all.
This winter we took him to hydro-therapy to rehab an injured leg. He swam in a heated pool specially set up for dogs 3x each week then 2x each week and after 12 weeks... he was performing perfectly again.  Here is why I mention that: He never produced that odor during or after those 12 weeks.  The pool was warm (80 degrees or more) there was also a 5 min session in a body temp hot-tub during each rehab session.
The odor began 2 weeks after he started swimming regularly in our lake again (I only allow him to go in when the air/water temp is reasonable)
I tried to give him a warm water shower after swimming to simulate the rehab process but that did not work either - the oder comes back within hours. I tried anti-dandruff shampoo... no luck there either.  Has anyone experienced something similar and does someone have a solution for smelly dog syndrome?  we sure would appreciate your input.  thx   Ted
Keywords: smell, smelly back, gland, secretion, oil, oily secretion, smelly secretion, glndular secretion, back smell, probable cause is cold water

Answer
Somehow this doesn't sound right.  I have never heard of a problem like that.  My 11 year old Aster swims into the colder weather with never a problem.  Of course she only gets to swim once a week or less.  I have friends that live on a lake and their Labs are free to swim whenever they want is it isn't frozen.  

Are you sure it is coming from his back?  Try his ears.  An ear infection can cause a general, foul doggy odor.  Fortunately some antibiotics will clear it up.  You may have to adopt an ear cleaning routine in addition.