the reconquista river in argentina is considered a " supercritical " river basin due to environmental degradation . within its valley of 1.547 km2 , there are more than 3 million inhabitants and 12,000 industries . using early - life - stage toxicity tests with bufo arenarum embryos ( the most sensitive of three native species ) 
 , we determined the water quality at six sampling stations of the river valley and expressed the results as acute and chronic toxicity units . 
 along most of the river , the toxicity was higher than the allowable level of whole industrial effluent toxicity recommended by u.s . 
 epa . in a tributary stream , arroyo moron , the water was about 10 times more toxic than the criteria maximum concentration ( cmc ) recommended by u.s . 
 epa for industrial effluents . 
 similar degradation of the water quality was found taking as a reference value an upstream sampling station . in all places where the water quality was worse than the cmc 
 , no macroorganisms were found , and in one of these places , a large number of dead fishes was observed . 
 our study points out that amphibian early - life - stage toxicity tests could be appropriate for assessing water contamination and water quality , which is essential for diagnosis , protection of environmental services , monitoring , and restoration purposes.imagesfigure 1.figure 2.figure 3.figure 4.figure 5.figure 6 .