My main swimming problems

Question
Hi my main problem is swimming fitness - although I am fit man which dry workout fitness was excellent but I struggled swimming abit cos my fitness still same at pool but wanna get fitter alot as olympics swimmers so how I do it? My freestyle, backstroke and breaststroke is good but I wanna swim faster as same speed as professional swimmers as Phelps, Lochte etc and finally, I struggled doing butterfly stroke (my strength is very good) like arm movements went fine but breaks down easily at 25m and cannot swim further at 50m, 100m and 200m etc. My butterfly/dolphin kick is poor cos I try do it properly, its speed was very slow like snail!! while I try get faster, my kick suddenly like bit of "mini" breaststroke kick which its annoying.

Answer
James-
Sorry it has taken so long to get back to you(slight medical problems).  It sounds like you are doing the right thing.  The main thing to remember is that being fit on land is great(aerobically), but once you jump into the water it's a totally different thing.  It took Phelps, Lochte, etc. years to get to the point they are at now.  Keep on working on your endurance in the pool and you can start getting faster, the more you train.  Don't get frustrated, improvement will come.
As for your dolphin kick, keep working at it, and concentrate on correct technique, it will come together.
Hope this helps,
George