The investigation was carried out between November 2004 and August 2005, and was based on the rivers Teusaca, Idaza, La Laguna (Quebrada Blanca), del Salteador creek, Marlene creek (affluent of the del Salteador creek), Blanca creek (Mataredonda-Reserve) and El Charco creek (affluent of Santa Barbara creek). All the rivers, with exception of the river Teusaca (Magdalena river basin), are part of the El Palmar river basin (Orinoco river basin). The waters are characterized by low conductivity (<52 μS cm-1), low temperature (11-14 °C), acid pH (5,5–6,3) and a high oxygen concentration (>90%). According to our field observations, some small forested areas still exist, and the soil is mainly used for agriculture (potato culture) and livestock farming.