Eco-toxicology is a potentially useful fusing of the two distinct disciplines of ecology and environmental toxicology. However, in applying an ambiguous "ecosystem approach," since the late 1970s, to the implementation of the Great Lakes Water Quality Agreement, there have been difficulties in delimiting the Great Lakes issues to be addressed under the Agreement and in ensuring that general biological resource management and conservation issues are dealt with separately under other existing mandates. There is a priority need for managers involved in the implementation of the Great Lakes Water Quality Agreement to decide whether the purpose remains one of maintaining and restoring Great Lakes water quality or whether it has already been transformed into a broad program to maintain and restore ecosystem integrity throughout the entire Great Lakes basin. Parts of this ambiguity may have arisen as a result of this fusing of ecology and environmental toxicology.