This
phenomenon is particularly observed from April
to December, when the plants cover almost com-
pletely the surface of water V´asquez, 1991.. The
water hyacinth produces undesirable effects in
the reservoir, because it affects the physicochemical
water quality, favors water lost through a
transpiration]evaporation effect, and screens
sunlight, affecting the underwater photosynthesis,
reducing the amount of dissolved oxygen and
therefore causing an imbalance in the food chain
of the species. The water hyacinth also houses the
mosquito Culex sp., a potential transmitter of
disease to the nearby population Avila-P´erez and
Zaraz´ua-Ortega, 1993a..