I couldn´t agree more with the swimming - it´s great and fun.

My training consists mainly of trail running, swimming and some strength conditioning, sometimes I add biking and other sports and activities.

I try mix the sports because 1. it´s fun and you will not get bored with only one 2. you cannot transfer your condition from one sport to another too much - for example a swimmer who doesn´t ride a bicycle would get muscle cramps in no time if he decided to do so. And conversely a biker who doesn´t train swimming would get cramps after several hundreds of meters in the pool. This is quite often underestimated fact by people who are specialized. Every activity engages different muscles in different ways. If a certain muscle is engaged in a new unusal way it will be overloaded very soon and you will get muscle cramps. So the only way to prevent this is to train the muscle this way repeatedly. If the muscle contracted and relaxed this specific way milion times in the past, it won´t be overloaded so easily next time.