Where does the river flow into, which starts at the Sierra Madre de Chiapas?
SELECT DISTINCT ?uri WHERE { ?x <http://dbpedia.org/ontology/source> <http://dbpedia.org/resource/Sierra_Madre_de_Chiapas> . ?x <http://dbpedia.org/property/mouthCountry> ?uri  . ?x <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/River>}
Sierra_Madre_de_Chiapas