I used to do a lot of swimming in younger years. As pointed out above, fast swimming it's all about efficiency and technique.
Front crawl is the only stroke to consider for long distance. Lost of tri swimmers and good amateurs never swim anything else.
Rather than just cracking out the distance each time you swim look to improve your technique and isolate parts of your stroke. For example, you might get a kick board so you only use your legs and a pull boy to you only use your arms and can really focus on good technique. You also want to make sure you learn bilateral breathing (every third stroke) so you stroke stays balanced. Learning to tumble turn fast and with power is also key. A typical training session might look like this.
1. Warm up 200 m front crawl
2. Main set 100 m with pull boy + 50 m kicking + 100 m full stroke. Rest 90 secs. Repeat 5 times
3. Warm down 200 m front crawl
You want to get a series of training sessions together to mix it up. Try and get a friend to film you so you can correct technique problems.
All that being said. After a while, swimming is boring as fuck and no substitute for lifting.
Edit: Remove unrequired info.
Front crawl is the only stroke to consider for long distance. Lost of tri swimmers and good amateurs never swim anything else.
Rather than just cracking out the distance each time you swim look to improve your technique and isolate parts of your stroke. For example, you might get a kick board so you only use your legs and a pull boy to you only use your arms and can really focus on good technique. You also want to make sure you learn bilateral breathing (every third stroke) so you stroke stays balanced. Learning to tumble turn fast and with power is also key. A typical training session might look like this.
1. Warm up 200 m front crawl
2. Main set 100 m with pull boy + 50 m kicking + 100 m full stroke. Rest 90 secs. Repeat 5 times
3. Warm down 200 m front crawl
You want to get a series of training sessions together to mix it up. Try and get a friend to film you so you can correct technique problems.
All that being said. After a while, swimming is boring as fuck and no substitute for lifting.
Edit: Remove unrequired info.