A new section of the Anacostia River Trail was opened in the fall of 2016, linking Washington DC's Anacostia Riverwalk trail to the Prince George's County network of trails. With the completion of this new 4 mile section of trail it is now possible to ride (or walk) trails from Nationals Stadium to the Bladensburg Marina and on to several trails in PG County.
The map below left was included in an article posted on Greater Greater Washington, a group that
runs a very informative site about the greater DC metropolitan area. Link to the article.
The Prince George's County Department of Parks and Recreation website includes this description of the new trail (link to source):
PG County Parks and Recreation has posted a video simulation of a cyclist traveling on the new section of trail: