We also observed an increase in the macrophytes cover during rainy months. Zooplankton biomass studies have been seldom conducted in Colombian lentic systems, but Gaviria (1993) found that crustacean biomass varied between 0.007 and 0.120mgDWL_1 (3.6-36ind.L_1) in the high-mountain Lake Chingaza, with the highest values occurring in the dry season.