Flooding is a critical global problem, which is growing more severe due to the effects of climate change. This problem is particularly acute in the state of São Paulo, Brazil, where flooding during the rainy season incurs significant financial and human costs. Another critical problem associated with flooding is the high level of pollution present in urban rivers. Efforts to address these problems focus upon three key research areas: river monitoring, modelling of river conditions and incident response. This paper introduces a rich next-generation middleware platform designed to support wireless sensor network based environmental monitoring along with a supporting hardware platform. This system has been deployed and evaluated in a real-world river monitoring scenario in the city of São Carlos, Brazil.