The next great river, the Sarapiqui, reaches the San Juan about twenty miles east of San Carlos. It is 600 feet wide at its mouth, and has numerous affluents from the sides of the volcanoes Poas, Barba and Irazú, the principal ones being the Toro Amarilla and Sardinal from the west, and the River Sucio from the east. The river is navigable for large canoes up to its confluence with the Puerto Viejo. Its banks as high up as to the River Sucio are low. The lands are extremely fertile. El Muelle Nuevo is the head of navigation, forty-five miles from the River San Juan and sixty-six miles by the road across the mountains from San José. From the Sarapiqui River to the River Colorado, a branch or bayou of the San Juan, the banks of the latter in Costa Rica are but slightly elevated. The lands are low and swampy, but occasionally a hill is found from fifteen to eighteen feet high. Below the Machuca Rapids the San Juan River is broad and deep as far as the junction with its Colorado outlet, about seventeen miles from the sea. Here it turns about nine-tenths of its volume of water into the Colorado. It is navigable for river steamers at all seasons, but has a dangerous bar at its mouth where the sea breaks heavily, and on which there are only from eight to nine feet of water. From the Colorado Junction to Greytown, some twenty miles distant, the San Juan averages about three hundred feet in width for sixteen miles and 100 feet for the remaining four, with a depth at high water of from six to eight feet. The Colorado has several islands in its course, but has excellent anchorage at its mouth. This river forms several lagoons which communicate with each other by caños or bayous perfectly navigable, the principal being the Agua Dulce, a short distance from the sea, eleven miles in length, 800 feet in width and from ten to forty feet in depth. Passing from the difficult Caño de la Palma in the midst of swamps, the Caño de Tortuguero is reached, the entrance to which from the sea is called Cuatro Esquinas. It is approximately thirty-eight miles long, about one thousand feet in width, with a depth of from fifty to sixty feet. The rivers Palacio and Penetencia, navigable for boats, empty into this caño. The River Tortuguero, which gives name to the plains watered by its affluents, is formed from several of these caños, as the Caño Desenredo, Caño Agua Fria and Caño de la Lomas. The Caño de Tortuguero communicates with the Parismina by the caños California and Francisco Moria Soto, which are also navigable. The margins of the Parismina are swampy. It has as its affluents the Guasimo, Camaron, Novillos and the Destierro. The lower district drained by the Tortuguero is raised but little above the ocean, and in flood time the river communicates by several caños with the Matina and with the delta of the Colorado, as well as with the lagoon of Caiman, lying south of the Colorado. Its numerous upper streams rise in the spurs of Irazú and Turialba.