Water in Knee - Recovery advice?

yogiamazon

I recently ran the Warrior Dash and apparently injured my knee in the process. A few days after the event, my left knee started swelling with no pain and it has stayed pretty much the same.
I know that it's just a matter of waiting it out and resting, but I was wondering if anyone else has had the same problem. Any advice? Is limited or toned down cardio still ok?