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The sampling of benthic arthropods is one of several common approaches to monitor and assess ecosystem health in both lotic and lentic systems. This type of environmental effects monitoring has a number of drawbacks that support the development of new methodologies to improve our ability to detect and mitigate effects in the field. We propose an enzymatic technique to assess the status of arthropod communities and ecosystem health rapidly and efficiently. The method is based on measuring the activity of free chitobiase, an arthropod moulting enzyme, in natural waters. The rationale behind using chitobiase activity and how it could be applied to general field monitoring and assessment situations are discussed. An example of results obtained from field level monitoring using this assay is presented from the Oir River catchment and one of its tributaries, the La Roche, in Lower Normandy, France. Chitobiase activity was detected and quantified with low variability in the Oir and La Roche with the enzyme's activity statistically related (p < 0.0001, r2 = 0.77) to standard water quality physico-chemical parameters using multiple linear regression. A decrease in chitobiase activity was noted downstream of a sewage treatment plant releasing effluent into the Oir. This is the first time chitobiase activity has been measured in a freshwater ecosystem as an indicator of ecosystem health. However, extensive validation is required before chitobiase activity can be used in an environmental monitoring context.