An observational study of suspended particulate matter (SPM) in the Irish Sea was carried out using AVHRR visible band and beam attenuation data. The satellite data consisted of a total of 165 AVHRR images covering the period between January 1982 to August 1988. The beam attenuation data were obtained from a summer and a winter mooring deployments at two sites in Liverpool Bay. The satellite imagery has shown that the surface reflectance due to suspended sediments varies throughout the Irish sea. The imagery has also shown that the reflectance undergoes a seasonal variation. The magnitude of this variation was assessed throughout the Irish Sea using a statistical model. The maximum reflectances occur early in the year and the minimum in the summer. The spatial distributions of the mean and amplitude of the annual variation have been shown to exhibit similar patterns. In some parts of the Irish Sea the surface reflectance was clearly seen to respond to the spring-neap tidal cycle. The spatial distribution of the annual mean is controlled by the availability of tidal turbulent kinetic energy (TKE). It was also shown that the availability of tidal TKE exerts a control on the seasonal variation and its spatial distribution. It is suggested that a further control is needed to explain the dependency of the seasonal variation on tidal TKE: a possibility is the seasonal availability of sediments. The beam attenuation data have provided further evidence of the seasonal variation of SPM concentrations at two sites in Liverpool Bay. An important finding from the in-situ data was the contribution of the wind to the seasonality of SPM concentrations in shallow waters.