Weekdays don't start until later in June, but the Ellen Linson pool in College Park has lap swim 6a - 9a. Beautiful pool.
http://www.pgparks.com/Things_To_Do/Sports/Aquatics/Ellen_E__Linson_Splash_Park.htm

Hi-- anyone know of early outdoor lap swim hours at a public pool? So far, I've only found Anacostia among the DC and Alexandria pools. Thanks!!