Four major rivers drain the numerous mountains of the Dominican Republic. The Yaque del Norte is the longest and most important Dominican river. It carries excess water down from the Cibao Valley and empties into Monte Cristi Bay, in the northwest. Likewise, the Yuna River serves the Vega Real and empties into Samaná Bay, in the northeast. Drainage of the San Juan Valley is provided by the San Juan River, tributary of the Yaque del Sur, which empties into the Caribbean, in the south. The Artibonito is the longest river of Hispaniola and flows westward into Haiti.