"lifting for strength (heavy weight, lower reps) will make you faster in the water if you have good technique."
Resistance training does produce changes in strength exercise performance and in the physiology of the muscles. However, its effects are specific to the training exercises and do not transfer positively to the sport for which they are "intended."
Some of the reasons for failure of land-based training are:
the resistance activities do not mimic the movement path or action speed of swimming;
muscular actions in the exercises are in coordinated patterns that have no commonality with crawlstroke swimming; and
the distributions of forces in land-training exercises are different to those of swimming.
The authors warned that land-based resistance training exercises may alter stroke mechanics.
That said, since this is a Master's swimming forum:
To thwart the decline in swimming muscle strength, masters swimmers should engage in land-strength work designed for the shoulders and arms to employ the muscle groups involved with swimming propulsion as well as tethered water swimming. The land work will likely have modest effects whereas the water work will be more beneficial.
Last sample regarding specificity: (strength is important but it has to be developed IN THE WATER so the technique adapts to the new levels of strength produced!)
Swimming strength is important. Upper body strength is a good predictor of success in swimming. If sprint swimming was correlated to power, and most events in swimming are sprints, the coefficients would be significant. Sprinters can be differentiated from distance swimmers by the power they can generate.
Using semi-tethered force measurement training responses can be monitored. After pre-season measurements are recorded swimmers typically get stronger. But then, as the training load continues to increase even more, arm power gets weaker. At the highest training loads, arm power is even less than in the pre-season state. Losing arm strength loses sprint capacity. Most coaches recognize this loss of strength with excessive training and program a taper so that power can be recovered. A taper enhances arm power recovery and performances.
How Much Training?
Costill has shown that a group of mature swimmers training once a day, when matched to a group training twice a day, recorded similar performance levels when both groups changed to training only once a day. The two-a-day group showed the classic loss of arm power and performance. At the same time the one-a-day group exhibited stable sprint performances. After taper, both groups performed similarly. What was the value in the extra work?
Does Land Strength Training Help?
Two matched groups of mature swimmers, one swimming only, the other performing dry land strength training, were tracked and measured. Both groups improved in swimming power and strength gains. The supplementary land training provided no added benefit. Costill attributes the lack of specificity in the land training to the lack of transfer. He stated: "You can gain strength by swimming. If you want to overload the muscle then do sprint swimming."