River macrophytes in regulated mediterranean-type rivers of southern Portugal

River macrophytes are frequently studied at fundamental or applied levels, such as water quality assessment and management. Though some effects of river flow regulation on aquatic plants have been documented for temperate rivers, few studies have addressed regulation in Mediterranean-type rivers. We compared the flora from regulated sites and reference sites located upstream from southern Iberian reservoirs. Contrary to other situations, species richness downstream the reservoirs did not present an increase related to flow regulation. Species richness was relatively similar on sites located downstream from the dam and on reference sites, but variability among sites was smaller for the former. Furthermore, the sites closer to the dam were the driest and developed a floristic composition typical of intermittent rivers when the latter presented sufficient flow to develop an aquatic vegetation. In many cases, this water availability is related to the influence of the hydropeaking discharges located a few kilometres downstream from the dam. The newly created habitats favour opportunistic species, which expand rapidly and modify the habitat.