In this article the diversity of environmental monitoring systems is studied. The number of such systems is steadily increasing each year, as systems are tailored to specific, growing needs of authorities, corporate users and citizens. Because of this, it becomes harder to compare systems and their functionality. Systems that appear to have the same functionality may turn out to be tailored for different application domains. Likewise, a chosen system may later on turn out to have insufficient support for connectivity and interoperability, although it provides the best support for core functionality requirements. To make sense of the ever growing diversity, and as the main contribution, a method for classification and analysis is proposed. The method is generic to environmental monitoring systems. The use of the method is also illustrated. The classification results yield even for a limited number of systems relevant clusters that help in identifying critical properties for further inspection.