For this pre-season swim session, focus on technique.

Work on making small improvements, even when you are tired, and use this as an easy recovery workout.
A:
600 warm-up with fins as 100 swim/50 kick, repeat
5 x 100 on 2:00 (25 right arm/25 left arm/50 swim)
6 x 75 with :15 rest (25 kick/25 non-free/ 25 free)
4 x 200 pull with :20 rest (25 scull/75 pull, repeat)
8 x 25 on :40 (catch-up drill)
6 x 75 with :15 rest (25 kick/25 non-free/ 25 free)
200 cool-down
Total: 3,200

B:
450 warm-up with as 100 swim/50 kick, repeat
4 x 100 on 3:00 (25 right arm/25 left arm/50 swim)
4×75 with :15 rest (25 kick/25 non-free/25 free)
3 x 200 pull with :20 rest (25 scull/75 pull, repeat)
6 x 25 on :40 (catch-up drill)
200 cool-down
Total: 2,100

C:
300 warm-up with fins as 100 swim/50 kick, repeat
3 x 100 with :30 rest (25 right arm/25 left arm/50 swim)
4 x 75 with :15 rest (25 kick/25 non-free/25 free)
3 x 100 pull with: 20 rest
(25 scull/75 pull)
4 x 25 on :40 (catch-up drill)
100 cool-down
Total: 1,400