Swimming can be an efficient, stressless, full-body workout, but not when you have to fight for lane positioning during lap swims at a public pool. That's why in summer your best bet is Lake Temescal on Broadway Boulevard in Oakland. Part of the East Bay Regional Park System, Lake Temescal offers a wide sandy beach, a snack bar, and an enormous sectioned-off area designated for serious swimmers only. Wade past the little kids and the tall guys who can't swim, plunge into the cool green depths, and chances are you'll be the only human swimmer sharing the waters with a few unimpressed ducks. And unlike at any of the public pools, you can swim your laps guilt-free while the lifeguards watch your kids.