Why is swimming distances difficult for me?

I am a runner and in great shape but i get so exhausted after swimming short distances. I know you work different muscles but id' really like to build stamina in my swimming. Any ideas on ways to keep going?

Why is swimming distances difficult for me?
endurance in swimming is a lot different than endurance in running. yes, your lungs need to be in good shape to do both, but swimming through water is a lot more difficult than running with just the resistance of air. the only way to improve it, is to swim a lot of distance. just start swimming and go for 20-30 minutes at whatever pace you can handle, and count how many laps you do. do this a few times a week and before you know it, you will be getting more and more laps done. its all about muscle memory. the more you do it, the easier it will be for your muscles.
Reply:i think what you should try to do is keep swimming. each day you should try to swim 2 more laps than the day before....it may be a slow process, but will most likely make you a much better swimmer.
Reply:Swimming requires, in my opinion, more muscle strenght than running. I have found out that myself. But, now, since I've been practising a lot, it is not as difficult as it seems. I have one advice for you:

Practice, practice and practice! At the end, you will find that swimming is not as hard as you thought it was.
Reply:I am a triathlete. I converted from running track and cross country in high school. I had a very hard time when I started swimming. Then I found a swimming coach that taught and trained triathletes. He told me that swimming was more like golf than running. Which really means is that swimming has more to do with proper technique than just powerring through. My coach taught us the Total Immersion way to swim. Once I learned the correct and most efficient way to swim, I felt like I could swim longer than I could run.
Reply:ok, I am a long distance swimmer, I do the 500 in races, which is 20 laps, but you need to have alot of practice try like swimming 20 laps non stop, breathe alot if you have too, in the races I am like taking 5 breaths a lap, and just breathe, and continue, just practice swimming for long distances, because you need to push yourself to swim them! I hope I helped!
Reply:It takes lots and lots of practice. You just have to swim a little more each day. I start out my swim season swimming 2 days a week for an hour, then i build up to 4 days a week for an hour and a half, and at the height of my season i'm swimming 6 days a week of practices for an hour and a half plus meets one day a week. So just build slowly. It really works.