Warming up, before the warmup?

I'm a newbie, to swimming for fitness, but not to general working out. I'm puzzled about how to make sure my aging bod is set for a good workout in the pool. I've always been under the impression that stretching cold muscles is not very productive, but I also don't think it's wise to drive to the pool, change, and hop straight in the pool and start doing laps. Do you stretch before you get in the pool (or er, intend to, anyway, most times lol?). Or does a hot tub do any good before a swim workout? It occurs to me that I'm beginning my swim workout "cold," and that it is maybe impeding my progress.