The objective of this study was to determine the effect of iron and zinc interaction on algal communities. Algal samples from three sources were used: Peoria, Farmington, and Princeton, all in Illinois. In general, it was found that zinc is much more toxic than iron. In the case of the Peoria samples, the effect of iron and zinc interaction was noninteractive in one case and antagonistic in another. In the case of the Farmington samples, these two metals are noninteractive against algal growth. To the Princeton samples, iron and zinc are synergistic.