The development of a fibre optic based system for the measurement of organic pollution in natural waters is reported. This system was designed to monitor organic pollution levels to warn of possible threats to the health of natural waters used as amenities and sources of drinking water. An experimental system was constructed to investigate fluorescence as a possible basis for an organic pollutant sensor. A systematic study was performed on laboratory prepared polluted water samples in order to identify the appropriate excitation and detection wavelengths. These measurements were compared and correlated with standard methods of analysis for gross organic pollution. Excitation and emission spectra were recorded on standard laboratory spectrofluonmeters. In addition measurements were made on a fibre optic based sensor characterization system. It was found that a linear relationship existed between organic pollution concentration and detected fluorescence when excited and detected at appropriate wavelengths Fluorescence detection was identified as a method for the measurement of Total Organic Carbon (TOC) concentration in water. A correlation co-efficient of 0 994 was achieved between TOC concentration and detected fluorescence signal for excitation at 340nm and collection at 420nm Limitations in the experimental system such as the expense and nature of the equipment meant that the experimental system was not suitable as a basis for a portable organic pollutant detection system. On the basis of this systematic study a dedicated optical fibre pollutant sensor for monitoring natural waters was constructed. This system used a higher power lamp, filters of appropriate wavelengths instead of a monochromator and high quality UV transmitting fibre. The performance of the prototype system was characterised in terms of range, resolution and response time.