Muscle Mass Effects

Hi, Until recently, rugby was my main sport, but a bad ankle injury means my playing days are over. While rehabing i spent a lot of time in the pool, on the bike and more recently on the treadmill. This type of training has interested me and I am looking at doing a triathlon next year. My cycling and running is not an issue but i find i struggle in the pool. I have spent the past 10 years between the pitch and the weight room and now I weight bout 270lbs at only 10-11% bodyfat so the majority of my bodyweight is muscle. I read somewhere that muscle doesnt float but sinks. Is this much muscle mass a bad thing when it comes to swimming? Thanks, Yak.