I tore the cartlidge in my knee so most exercising is out. However, we have a 3 1/2 foot deep pool for my daughter. I was thinking of buying a "noodle" chair (im not sure if I can post links or not) to sit in and use it to tread water. Think that would work?
Seems like any kind of movement would be better than nothing, if it's safe for your knee to do that. Can you walk in the pool even? Even just walking in circles around the pool would be great too if your knee can handle it.