Canal de Castilla Rey (Palencia), considered the beginning of the Northern Branch, Valladolid and Medina de Rioseco, lying at the end of the Southern Branch and Campos Branch respectively. The countryside crossed by the canal is of interest for its birdlife. In the Tierra de Campos there are two large Special Protection Areas ("La Nava-Campos Norte" and "La Nava-Campos Sur") which are notable for the birds such as great bustards ("Otis tarda") which live in the dryland farming areas (sometimes described as "steppes") which are typical of the region. The canal, on the other hand, provides habitats for wetland birds such as the
Edwardsiella tarda along with maintaining suitable sanitation of water. Other stress factors include drastic changes in temperature, pH, and dissolved oxygen levels in the water. In order to manage properly for edwardsiellosis water must be checked constantly in order to keep fish stocks completely free of pathogens. Some of the most recent research done on "Edwardsiella tarda" was performed by Griffin et al. (2013) to assess what the literature refers to as "the intra-specific variability of "E. tarda" isolates from 4 different fish species in the eastern United States." These intra-specific variations that they were looking for occur in other parts of