The only triathlon held in Washington, DC is gearing up for its 10th annual event, and 15 triathletes have participated every year. Events DC Nation’s Triathlon To Benefit the Leukemia & Lymphoma Society will take place on Sunday, September 13, 2015. Triathletes can register at NationsTri.com, with opportunities to join one of the many races-within-a-race challenges—ranging from military to congressional challenges.