True flies (Diptera, Insecta) are one of the most important groups of aquatic insects in respect of the number of families and abundance of individuals. The goals of this study were to determine emergence patterns and the main ecological factors that influence dipteran family abundance and emergence at barrage lake outlets. Differences in abundance and variations between microhabitats were examined. The study was carried out in Plitvice Lakes National Park (Dinaric karst region, Croatia) at outlets of three barrage lakes. On each site several microhabitats, which differ in substrate and water velocity were selected. The selected substrates were moss on tufa, particulate tufa with detritus, pebbles and silt. Sampling of dipteran adults was conducted at the end of every month during 2007/2008 with 6 emergence traps placed at each site. Simuliidae and Chironomidae were the most abundant families among the 13 families present. Temperature influenced the start of emergence and the duration of flight period. All three lake outlets differed in abundance of individuals, especially the lowest barrage lake outlet which can be contributed to the lowest levels of organic seston and highest rates of tufa deposition. For Chironomidae, Simuliidae and aquatic Empididae statistically significant positive correlation between abundance and current velocity was observed. The least favoured substrate for all Diptera families was silt, while moss was the preferred one.
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