The study was developed in four contrasting streams (Qbda. Ancha, Qbda. Limón, Chilibre, Chilibrillo), during the period September 1999 – may 2000, in order to use ‘Asociaciones Potencialmente Indicadoras, API’s (‘Potentially Indicator Associations’ e.g. CHIRO, EPT, MOL, HOT) to discriminate streams with different water quality. A 25m long study site, was established in each stream, where three leaf packs were taken monthly. Samples from Qbda. Ancha were dominated by CHIRO, MOL, HOT, whereas Qbda. Limon, Chilibrillo, and Chilibre by CHIRO, EPT, and DEP. Cluster analyses showed that Chilibrillo and Chilibre were the most similar sites in taxocenotic terms, though Qbda. Ancha was the most different. Similar pattern was showen when using physico-chemical data.