The Medellin River is the main body of water in the Aburra Valley in Colombia. It is a highly polluted river, which is now in the process of being cleaned, under a program being executed by EPM, the local state-owned utility. The environmental authority in the Aburra Valley region is the AMVA (AREA METROPOLITANA DEL VALLE DE ABURRA), which has overseeing power to regulate emissions to the river and to attain the required water river quality, as demanded by the existing regulations. As the Aburra Valley is an area where near 4.0 million people live, being also an important industrial, commercial, financial and educational center, the pollution loads are sizable. Given that the existing water treatment system is clearly insufficient, the water quality of the river is poor. AMVA contracted a group of four local universities to develop a very complete and complex study and set of data, to characterize the river and to understand its environmental situation in an integral and comprehensive way. This article uses a previous study of this set of data oriented towards establishing quality indexes based on temperature and oxygen demand, to establish correlations with biological information gathered in the AMVA study, in the case of macro invertebrate specimen data. It is concluded that there is a clear correspondence between the abundance of individual macro invertebrate specimens and the water quality.