In the present work a limnological evaluation was made with special emphasis on the effect of concentration of pesticides on fish and sediments in tradicional rice crops areas near of the rivers Ariari, Guayuriba, Humea and Meta in the Orinoco Basin (Llanos Orientales). The sampling areas showed interesting physicochemical characteristis wich magnify the effect of pesticides upon the biotic comunities. Based on these parameters and the biotic differences e dueto diversity and richness of species ), the area was grouped into two sub-systems, one of wich presented increaing signs of eutrofication. · The information recorder sic e 1980 shows that the fish comunities present preocupating hazardous in crease ofpesticide specially aldrin-dieldrin and metilparation in concentrations wich exceed those stablished by FAO/OMS.