At one time it was closed but I understand that boating is now allowed. However, I believe that you have to check-in with the Park Police--the office near the intersection of Beech Dr and Military Rd.
   The question is why would you want to run it? There is a lot of urban debris in this stream when it floods. In addition to the usual trees, etc, I have seen a lot of picnic tables, sign posts, fencing and other assorted garbage. The creek picks up a lot of chemical (mostly petroleum from the streets) runoff during heavy rains and DC's sewage system overflows into the storm drains during periods of high flows. The stream doesn't smell very good even during the best of times.
   For 15 years I've lived close enough to easily carry my boat down to Rock Creek and I drove along it every day for 9 years; I've never seriously considered running it because of all the crap (literally and figuratively) in the stream. Surely, there's got to be better places to go boating than this.