Mexico City is a densely populated area that requires a number of water sou
rces to satisfy the demand. The water level in the wells within the city is
very low, and the water quality has decreased over the years. The Valle de
Brave Reservoir supplies the Los Berros treatment plant (capacity, 9 m(3)
s(-1)). This study considers evaluation of V. cholerae in the fish communit
y in the reservoir as an indicator of the microbiological water quality.