Non-weight bearing, ideal if you have a bone-related problem. Ex-Harey Olympian Andy Baddeley explains the benefits of swimming for runners here, whether injured or not.
You can replicate your running training and plan some sessions (to make it slightly less boring), potentially mixing it up with pull buoys and kick boards to focus on your upper and lower body endurance/strength respectively. Even if you’re uninjured and running, an example of an active recovery session in the pool could be: 20 lengths easy front crawl, 2x[6 lengths with the pull buoy, 6 lengths with the kickboard], 20 lengths easy front crawl.
If you’re likely to be injured for a while, it might be worth joining CUTriC (the triathlon club) for their swimming sessions for a bit of company.