Finally, in order to evaluate water quality, we estimated
the BMWP/CR index, for each treatment and sampling point
(Fernández, 2002; Mafla, 2005; Roldán, 2003). The BMWP/CR
(Biological Monitoring Working Party adapted for Costa Rica by
Martínez et al.) is an index that is calculated by accumulating the
pre-assigned, values of sensitivity to water contamination for the
various macroinvertebrate families (Tables 2 and 3). Based on this
score, six levels of water quality have been established (GACETA,
2007). This index is currently recognized as the official index to
monitor water quality in Costa Rica.