Human fishing activity as a source of disturbance for waterbirds on Thale Sap (Lake Songkla, Thailand) was studied during June/July and October 1987. The distribution of fishing activity was compared with that of birds. Fishing activities were observed to quantify the incidence of disturbance interactions, and disturbance caused by local fishing craft was investigated experimentally. A variety of fishing methods were used in the main lake habitats (Paspalum, Scirpus, and open water), particularly in early morning and late afternoon. Many birds use these habitats at the same times, although there were some relatively undisturbed areas, e.g. the centres of Paspalum mats. While disturbance of birds was seen relatively infrequently, some fishing methods (e.g. beating into seine nets) were very disruptive and most birds probably fled as soon as fishermen arrived. Experiments confirmed that boats were a significant cause of disturbance, although less so in habitats with more cover. There were also marked differences between species. Longer-term studies are needed to determine whether the current level of human activity, and possible developments such as increased recreational use of the lake, are consistent with conservation interests.