Not sure now bad your knee is but have you tried or heard of aqua running/jogging? It\'s still in the water but it would be a different kind off work out, and it may also reduce the risk of impact on the knee.
There\'s also the chance that you could work on your \"core” with stretches and certain weight exercises maybe?
Hope this helps some how.
By the way are you a member of Edinburgh tri or the Road Club?