Rideau Canal Skateway, Ottawa, Ontario
In today's earlier entry on skating rinks, Alex B. and Charlie comment, rightly, that DC tends to not sustain temperatures cold enough to freeze and maintain ice rinks without refrigeration.
Charlie mentioned the C&O Canal as a possible option. In Ottawa, it being much colder, they do use their frozen canals as winter open spaces.
-- Rideau Canal Skateway, National Capital Commission