Exercise with a boot!

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I had foot surgery last December - was "freed" to go back to running in February. Going along good and about 2 weeks ago I injured my foot. Not sure if its a fracture or a strain either way apparently my surgery has not healed yet. So I am back in the boot for a month and no impact exercise - no running or jumping. So looking for suggestions to get this stupid foot healed and not injury anything else but keep active. Anyone been in my situation have some good cardio exercises? I did just join a gym and I went to the pool last night too. Anything else?