Extreme weather events strongly influence chironomid structure even in an artificially regulated reservoir

Interest in climate change-related water level fluctuations and their effects on aquatic communities has increased. Chironomids are reliable indicators of extreme conditions, yet it remains unclear whether climate-induced compositional changes occur in lakes with artificially regulated water levels, such as Lake Tisza. We studied the direct and indirect effects of hydrological extremes and climatic factors on chironomid assemblages from 2009 to 2022, hypothesising that extremes drive compositional shifts and reduced diversity, with indirect effects more pronounced. Results confirmed this, revealing a remarkable assemblage change over 14 years. Flooding during the vegetation period significantly altered habitat diversity, causing notable structural changes in chironomid assemblages. Compositional variability was more closely linked to environmental variables than to discharge or climatic variables. Oligotrophication emerged as the main driver of long-term trends. Diversity responded to environmental changes, declining after summer floods, but recovery was rapid, with no lasting diversity loss despite structural shifts. Projected increases in climate extremes suggest further alterations in chironomid composition and diversity. These processes may ultimately affect the food web and compromise the lake’s conservation function.