Monitoring and early warning of water pollution play a very important role in prevention and response to pollution incidents. Monitoring and early warning information, if provided regularly in real time, will help detect pollution and saline intrusion incidents in advance, thereby proposing timely response solutions. In this paper, we introduce a monitoring and early warning system for water pollution incidents developed for Gia, Re and Da Do rivers in Hai Phong. The system consists of hardware and software sub–systems, in which the hardware is the monitoring, transmitting and receiving devices as well as server that provide information about water quality in real–time. The software includes a database management system, an pollution early warning tool, a data quality control and analysis tool and a website providing water quality information based on webGIS platform. The system is capable of providing complete information about the current quality status on the GIS platform, including: Water quality from periodic measurements, real–time water quality and discharge and pollutant concentration of pollution sources. The developed system has provided very useful informat