This extension of the trail is not yet officially open, but there were many people riding it. We started just north of Benning Road and turned around at the Blandensburg Waterfron Park. The trail passes the Kenilworth Aquatic Gardens and some very lovely sections of river and wetlands. It looks like it could be completed in the next 4-8 weeks. In the meantime, ride the section that goes from RFK to the Nationals Stadium: https://wlerik.wordpress.com/2013/09/08/anacostia-river-trail-loop/
Access trail 100 yards north of Benning Road from Anacostia Ave (see green marking on photo below).