This canal is one of the most important hydraulic engineering works carried out between the mid-18th century and the first third of the 19th century in Spain. It runs through part of the provinces of Burgos, Palencia and Valladolid in the autonomous region of Castilla y León, and was built to facilitate the transport of wheat from Castile to the northern ports and from there to other markets. However, with the arrival of the railway, it became obsolete.

It was originally conceived as a network of four canals that would link Segovia with Reinosa, but due to its enormous technical difficulties and enormous resources, only three branches were built. With a width that varies between 11 and 22 metres, the canal runs for 207 kilometres, crossing 38 municipalities and linking the towns of Alar del Rey, where it has its source, with those of Valladolid and Medina de Rioseco, located respectively at the end of the South and Campos branches, so that the Canal has an inverted Y shape. Moreover, it has a total gradient of 150 metres.

Curiously, the province of Palencia is the one with the longest canal, where the North branch is located. A few kilometres to the north of the capital of Palencia, the canal divides into two large branches, one going to Medina de Rioseco and the other to Valladolid, where the southern branch is formed.

As it passes through the city of Palencia, which it approaches by means of a small branch ending in a dock to facilitate loading and unloading, the Canal de Castilla is located at a short distance from two of its most emblematic points: Calahorra de Ribas, where it crosses the River Carrión, from which it takes its water, and the Serrón, in Grijota, where the canal forks into the Campos and Southern branches.

Today, this great inverted "Y", which runs from north to south through the Castilian and Leonese autonomous region, conserves a valuable network of locks, flour mills, warehouses and docks of great historical interest. It also provides water supply to urban centres, irrigation for the countryside and a cultural and leisure space for locals and visitors. Various investments are being made to recover it and give it an outlet for rural tourism, at the same time as its towpaths are being developed as cycle routes, as various riverside ecosystems have emerged on its banks, with a first strip of hygrophilous vegetation formed by reeds and cattails, a second strip similar to a gallery forest (elms, black poplars, white poplars, ashes, willows, alders, honeysuckles...); and a third strip of bushes. Among the fauna of note are marsh harriers, numerous ardeids, anseriformes and Podicipediformes, among others.

Over time, a series of wetlands of high ecological value have formed on the banks of the Canal de Castilla, representing an island of biodiversity within the homogeneous landscape of Tierra de Campos. These wetlands vary in size: some are less than one hectare in size, while others cover more than 20 hectares. Their high ecological value is related to their diverse aquatic vegetation and the large number of vertebrate species they are home to.

Among the birds, in the Canal there are 121 species of nesting birds and also wintering birds and migratory and accidental birds; 42 species of mammals, 15 of them insectivorous; 11 species of amphibians and 14 species of reptiles and 14 species of fish. These environmental values have led to their inclusion in the Natura 2000 Network, as most of the wetlands have been declared Special Protection Areas for Birds and Sites of Community Interest, and are also included in the Regional Catalogue of Wetlands. However, this degree of protection has not been sufficient and currently the lagoons of the Canal de Castilla are in a deplorable state of conservation and some have even disappeared.