Abstract There are three major lagoons indenting the shoreline of Tunisia. The Lake of Bizerte on the north coast of Tunisia is in the Mediterranean climatic setting. The Lake of Tunis, 50 km to the south, is in a semi-arid climatic setting. Bahiret el Bibane, 450 km south of the Lake of Bizerte near the Libyan border, is in an arid climatic setting. The summer salinities of the three lagoons reflect the climatic differences. Man has had an impact on the two northern lagoons. The Lake of Bizerte outlet to the Mediterranean has been deepened by dredging. The Lake of Tunis has been altered through infilling by man (an ongoing process), construction of a diked ship channel, and introduction of large amounts of raw sewage. Bahiret el Bibane is relatively unaffected by the activities of man. The sediments in the Lake of Bizerte are dominated by mud-size clastics from intermittent streams draining farmland; in addition, there is an important biogenic component. The most abundant sediment in the Lake of Tunis is an organic-rich terrigenous mud derived from the adjacent drainage basin, but biogenic productivity is high and forms a locally dominant sediment component. Calcareous worm reefs flourish because of the high nutrient content. Summer eutrophication is frequent. The sediments of the semi-restricted Bahiret el Bibane are dominated by biogenic fragments (mostly mollusks) but with an important wind-transported detrital component. The north to south changes in the character of the clastic sediments of the Lake of Bizerte and Bahiret el Bibane are mainly related to the source of the sediment which is largely controlled by climate. The influence of man dominates sedimentation in the Lake of Tunis.