This book chapter introduces a European Union-backed water quality monitoring and early warning system implemented in the cross border region of Hungary and Slovakia achieved by Hungarian and Slovak partners. The measurement system consists of buoys which carry sensors and send measurement data wirelessly to a gateway on the riverside. The gateway transmits the data to a server, where it is saved and processed. Based on the collected data, alerts can be sent in case of anomalies. Utilizing this solution, an early warning system for water pollution can be deployed, which decreases water quality monitoring costs.