Once upon a time, many rivers flowed over the island of Montreal. Why did they disappear? How? And could we see them again? Explore an ephemeral urban history with this iPhone app.Connected to the documentary film of the same name, Lost Rivers is a playful but enlightening mobile application for urban dwellers to discover the lost rivers of Montreal, Tapping into locative media technologies and augmented reality, the application offers a new means of engaging with the urban environment through interaction with virtual landscapes of the hidden past and of the imagined future. Like a digital dowsing rod, the iPhone app allows users to locate the many ancient watercourses that still flow beneath the streets of the city. The app uses the devices GPS system to reveal a lost river below a users feet in real time, and to trace out the paths of rivers, pre-diversion, over the contemporary city grid. The application interface links specific geographic hot spots" loaded with fascinating historical lore, urban legends, 3-dimensional soundscapes, photos, and extracts from the documentary film.