In the very center of the Republic, surrounded on all sides by lofty mountains of the central group, is Constanza Valley, rich but to-day almost inaccessible. No less rich, but many times larger, is the other interior plain, known as the Eastern or Central Valley, a succession of fertile valleys, extending from the Neiba River to St. Raphael, almost 115 miles, with a width of from nine to twenty miles. The entire plain is claimed by the Dominican Republic, but more than half is in possession of Haiti.
All these various valleys and plains enjoy the advantage of being watered by a comprehensive network of rivers of greater or less size. Many of the streams are navigable for miles in the lower part of their course by boats and canoes, affording means of communication to which the wretched condition of the land highways gives added importance.
The largest river of the Republic is the Yaque del Norte, some 240 miles in length, which rises on the slope of Yaque Peak, describes a circuitous northerly course, receiving numerous mountain affluents, until it reaches the vicinity of the city of Santiago de los Caballeros, whence, turning northwesterly it flows through the Santiago Valley, being reinforced by scores of tributaries. Its waters are finally discharged partially into Monte Cristi Bay and partly through its many mouthed delta into Manzanillo Bay. Detritus and driftwood brought down by the river, for many years entirely filled the Monte Cristi channel, and still constitute barriers which cause large lagoons to form in the delta and to inundate extensive tracts of rich farmland. Though the bars at its entrance render the river inaccessible for larger boats, it is navigable for canoes over its entire course in the Santiago Valley.
Another large river is the yellow Yuna, which waters the eastern part of the Cibao Valley. Rising in the mountains near the center of the Republic, it directs its course to the Royal Plain where it receives the waters of the rapid Camu, and thence flows eastwardly and enters Samana Bay through a marshy delta, its total length being over 200 miles. Part of its waters find their way through the great swamp, the Gran Estero, into the Atlantic Ocean. Up to its junction with the Camu, a distance of some 30 miles, the Yuna is navigable by boats and barges, and above the junction both the Yuna and the Camu are navigable by canoes for nearly 30 miles more though there are shallow stretches where the streams run rapidly and great care is necessary. In former days, the Yuna was one of the chief outlets of the Cibao; freight and passengers were transported over its course to Samana Bay and on the waters of the Bay to the town of Samana where transshipment to larger vessels took place. With the establishment of the railroad from La Vega to Sanchez, the river has lost much of its old-time importance.