Workout

Warm-up (600)
400 swim, 200 kick

Set (400)       
2 rounds
4 x 50 on :50,:50, 1:00, 1:20 
1) easy-fast (build)
2) fast-easy (reverse build)
3) easy (recovery)
4) fast (fast!!!)

Set (800)       
2 rounds
2 x 50 -count strokes
4 x 50 -6R / 6L / 6 swim drill
2 x 50 -count strokes'
 
Set (1200)
4 rounds        
1 x 200 swim @ 80%     
1 x 50 kick @ 90 %     
1 x 50 swim @ 100%     
...take 10,10, 1 min rest between rounds

Cool-down (200)
100 kick
100 swim