The goal is to have more than a million river watchers along the Yangtze in the next three years, which is citizen science at an unprecedented scale. However, the corresponding data management challenges for river observation are daunting. To have trust in water samples or data collected by lay observers, the data must be supported by adequate metadata. Metadata have always been the weak link of citizen science. However, an estimated 5 billion people globally have some sort of cell phone and the phones are pretty much smart enough to tag data with the who, what, when, where, and how that are needed to provide meaningful context. There may be few places in the world that have the population density of China, but there are also few places that can afford not to learn something about citizen science from this large-scale experiment.