Where does the river end which starts in Richmond Park?
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/sourcePlace> <http://dbpedia.org/resource/Richmond_Park> . ?x <http://dbpedia.org/property/mouthLocation> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/Stream>}
Richmond_Park