Hi Warkat. It may be possible to get these questions answered by phone. If you've tried calling the surgeon and/or physio without a response, my feeling is that water aerobics would be fine. With grade 4 chondromalacia and a recommendation of cartilage repair surgery, I was still cleared to swim. Water aerobics should unload most of your body weight from the knee joint, and my understanding was that unloading is the main thing to do to protect the joint. Until you get treated, don't push through pain, avoid movements that hurt, and try to minimize unnecessary weightbearing and especially pivoting on that leg. If you've done quad sets and straight leg raises in the recent past, those are probably also good ways to strengthen the quad above the injured knee and help keep your weight up and off the joint. This is based solely on my own experience, so I hope others weigh in as well.