Self-sustaining ecosystem microcosms, called ecosystem jars, can easily be collected from local ponds, streams, or lakes. Sealed and exposed to sunlight, these miniature ecosystems can sustain themselves for a decade or more. Unlike Winogradsky columns, ecosystem jars are optimized for protist, animal, and plant observations and experiments, and are not altered by addition of sulfur, carbon, or cellulose sources, more accurately representing natural ecosystems. Ecosystem jars can support a variety of inquiry-based experiments, including student-designed projects, from middle school to college levels. Students, with instructor assistance, formulate hypotheses, design experiments, observe and catalog organisms by microscopy, then record their data in tables and graphs and draw conclusions. Students present their data in a paper or poster format or as oral presentations to the class. Potential experiments include examining biotic changes over time, the effects of added pollutants or nutrients, biotic differences between watershed types, or seasonal changes in biota. These investigations not only provide students with cooperative learning, inquiry-based lab experiences, but also help them gain appreciation for the effects of pollution or nutrient runoff on ecosystems.