Question: Name the river with source as Columbia Lake and river mouth is located in Clatsop Country ?
SPARQL:
SELECT DISTINCT ?uri WHERE {?uri <http://dbpedia.org/ontology/riverMouth> <http://dbpedia.org/resource/Clatsop_County,_Oregon> . ?uri <http://dbpedia.org/ontology/source> <http://dbpedia.org/resource/Columbia_Lake>  . ?uri <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://dbpedia.org/ontology/River>}