Landfill leachates are composed of a complex mixture of degradation products which include a wide range of potentially fluorescent organic molecules and compounds. Here we investigate the use of fluorescence excitation-emission matrix (EEM) analysis in detecting diffuse landfill leachate contamination in rivers. Landfill leachates from three unlined landfill sites adjacent to our study river are characterised by intense fluorescence at excitation wavelength 220-230 nm, and emission wavelength 340-370 nm, which derives from fluorescent components of the xenobiotic organic matter fraction. Seven surface water sample sites on an adjacent polluted river system were analysed for fluorescence and water quality properties. The 220-230 nm excitation wavelength, 340-370 nm emission wavelength fluorescent centre was also detected in this river system at the sample locations downstream of the landfills, but not at upstream control sites, demonstrating its use as a tracer of landfill leachate contamination. Negative correlations are observed between this fluorescence centre and dissolved oxygen in the river water samples, demonstrating the water quality implications of leachate contamination at this study site. The fluorescence intensity at the 220-230 nm excitation wavelength, 340-370 nm emission wavelength fluorescent centre in landfill leachates is such that it remains detectable at dilutions of 10(2)-10(3), and the fluorescence EEM technique is rapid and cost-effective for use by river managers and water quality regulators.