Changes in aquatic and marsh vegetation at Lake Zeribar in the Zagros Mountains, Iran, during the last 40 000 years were reconstructed on the basis of plant macrofossils. Several episodes of low water level and increased salinity were evidenced by peaks of Chenopodium rubrum seeds and the occurrence of obligate (Salicornia sp., Ruppia maritima and Suaeda sp.) and facultative (Zannichellia palustris) halophytic macrophytes as well as brackish water and marine diatoms. Some of these events can be correlated with an increase in diatoms indicative of higher conductivity and with changes in oxygen-isotope data. They are interpreted as the expression of general climatic dryness, although water-level changes might also have resulted from episodes of deposition on the alluvial fans that dam the lake. A few such water-level changes occurred in the Pleniglacial. The most pronounced lowering corresponds to the Younger Dryas interval of high climatic aridity. Macrofossil indicators of water-level changes appeared also in the Holocene section of the profiles at the same time as Quercus expanded on the surrounding uplands, culminating about 6000- 5000 14C yr BP, giving support to the hypothesis that the delay of forest expansion in this part of the Zagros Mountains was caused by climatic dryness.