Workout

Warm-up (900)
300 swim/100 kick
200 swim/100 kick
100 swim/100 kick

Set (200)
4 x 50 build on :50

Set (1500)
6 rouds
100 on 1:30
75 on 1:10
50 on :50
25 on :30
...increase speed as distance decreases

Set (400)
16 x 25 sprint on :30
...kick or swim

Cool-down (200)
200 easy