Best cardio exercises for a human being beside knees injuries?

I love working out and I enjoy cardio of adjectives types..... running, power walking, step classes, boot camp classes, egg-shaped trainer and treadmill. But I recently hurt my knees and the doctor suggests that I do exercises that do not put my weight on my knees. I enjoy mass lifting but I know that I must mix that with some sort of cardio to allege balance... Please backing, all suggestions are welcome.Best cardio exercises for a human being beside knees injuries?
I can share with you some tips base on my some of my PT clients experience. However whatever it is, the most momentous thing is to listen sttentively to your doctor (ex. if your doctor saya a individual exercise have to be avoided, later listen to his advice). Basically, if you have knees pain, it is best you rest and get better first before attempting any exercise. After that, you can start near some low impact, or non impact type of workouts. Low impact workouts means as long as in that is still one ffot in contact next to the ground (ex. walking). You may also try non impact workouts (both foot in contact near the floor) like the egg-shaped trainer, but do limt the angle of knee flexion first.
In adding together to that, you may wish to consider wet based workout (ex. aqua aerobics, or walking/jogging contained by the pool). In fact, marine based exercises are best for culture who have combined injuries or problems; a good agency to workout as well.
SEX that is to say if you are over 18 and you must be an active participant lol