This study was carried out to analyze the levels of oxygen evolved in catalase activity during hydrogen peroxide decomposition reaction in species of different aquatic macrophytes and their selected families, Pontederiaceae, Araceae, Lemnaceae, Ceratophyllaceae, Azollaceae, Nymphaeaceae in two different Rivers in Delta and Edo State. Hydrogen peroxide is formed as a toxic waste product of metabolism which is quickly converted into other less dangerous chemicals. It is an important signal molecule involved in plant development and environmental responses. The enzyme catalase is frequently used to rapidly catalyze the decomposition of hydrogen peroxide into a harmless molecule of oxygen and water. Anthropogenic activities of excess nitrogen and phosphorus nutrient enrichment into water body proliferation result in eutrophication, which most species of aquatic microphytes can use to control them. The catalase levels in species of Eichhornia crassipes followed by Eichhornia natans in Pontederiacea family recorded the highest in their leaves (24.83 ± 0.29) in Ethiope River and (24.20 ± 0.10) in Ikpoba River respectively among the aquatic macrophytes studied. Those species under the family Nymphaeaceae had (23.73 ± 0.64) as in water lily in their leave tissues in Ethiope River, followed by the family Ceratophyllaceae which had (20.33 ± 0.58) in Ikpoba River, Edo State. The lowest catalase activity was recorded in the roots of Azolla africana and Nymphaea lotus (12.00 ± 0.05) and (12.30 ± 0.10) in Ethiope and Ikpoba River. Catalase enzymes present in these species of aquatic macrophytes are useful in commercial cleaning operations in bioremediation for aquatic and terrestrial ecosystems.