an area of 129 632 km2. The river receives urban
wastewater discharges from 29 municipalities, as
well as industrial water discharges, both treated
and untreated, mainly from the industrial zones
of Toluca, Lerma, Ocoyoacac, Santiago Tianguistengo,
Pastej´e and Atlacomulco. It is estimated
that during a year, the stream receives 536=106
m3 of waste waters, which carry 350 946 tons of
organic load; 33% of these waste waters come