Two times a week does not cut it. Athletes who come from a strong swimming background can get away with this as a way to maintain most of their form and a lot of their speed. However if you are new to swimming, you are going to have to put more time into it than they currently do.
The person you are watching swim laps effortlessly at a fast pace at your local pool has put hundreds of hours into the pool, and you are witnessing the end result of all that work.
That's at least three times a week, and ultimately, you want each session to be an hour or more (roughly 3,000 yards or meters). You can ramp it up in the winter when it gets cold, and you are not spending long hours on the bike.
Remember, this article is about how to swim fast, not how to swim, period!
Jumping into the pool and swimming laps until you're tired or bored just became how you used to swim. You're now going to graduate to structured workouts, like real swimmers use. Almost every swim workout you do should be structured, and each week should include workouts that target various systems like an aerobic workout (longer), a muscular endurance workout (mid-distance and moderate hard).
The exceptions to pure structured workouts are steady open water endurance swims or non-stop simulation swims in the pool, and those are structured in the sense that they're included in the top-level organization of your training.
A typical swim workout should include the following components (example provided)
10-15 percent easy warming up (4x100 easy on 20 seconds rest)
10-20 percent drills and kicking (8x50s as alternating 1 drill, 1 kick on 15 seconds rest)
- 40-70 percent main set (6x200 on 30 seconds rest or 12x100 on 15 seconds rest)
Optional additional drills
5-10 percent cool down (100 easy)
The main set is the meat and potatoes of the workout. Each main set should have a specific training goal: endurance work (longer swim intervals), speed work (short, fast intervals) or muscular endurance work (medium length intervals at moderate-hard effort levels).
If you're training for an Ironman, doing nothing but long, slow intervals will prepare you to swim—albeit long and slow. Short and fast will help you become a faster swimmer, and that speed does flow through to longer distances in swimming.
Improve your swim with a masters swimming program.