Workout 2
The ideal way to divide up a 30-minute workout is to do 10 minutes warm-up, 15 minutes main set, and five minutes cool down. Depending on your swimming ability, you may cover anywhere from 1,000 to 2,500 meters, so the workout below has room for variation according to your ability (it will cover 1,800 meters).

Warm up:
300 meters (five minutes)
4x50?s kick/swim (IM order) @ 1:15

Main set:
400 @ 5:30
300 @ 4:45
200 @ 3:00
100 @ 1:30

Cool down:
300 meters (backstroke, breaststroke) (five minutes)