The Yarlubb river was on the forest moon of Endor, flowing somewhere between Bright Tree Village and Red Bush Grove. Leektar once followed this river during his search for another village after his own was destroyed.
Behind the scenes
Yarlubb river was a location developed by Arthur Papadam as part of Leektar's What's The Story? entry.
Sources
Leektar's Story: Everything you didn't need to know! on We'll Blow Your Planet Up! — Arthur Papadam's StarWars.com Blog (original site is defunct)
Leektar in the Databank (original site is defunct)