To celebrate a special Open Access issue of Hydrology Research journal – "Advances in Research on River-Lake Interaction and Impacts" – issue organiser Qi Zhang discusses the importance of this topic to ongoing research.

Increasingly intensive human activities have been altering the hydrological connections of river systems significantly and have become the focus of hydrology research in the last decade. Construction of hydraulic engineering on rivers is among the strongest of human interferences to the river systems. Research into the impacts of such human activities on the hydrology and ecology of river systems is of significant importance to improve our understanding of the interactions between human activities and river systems. The Yangtze River is the largest river in China and the third largest in the world, with an average annual runoff of 9,970 x 108 m³, accounting for about 40% of the total river runoff volume in China. The Yangtze River has been attracting a large amount of research both domestically and internationally. The construction and operation of the Three Gorges Dam (TGD) in 2003, the largest hydraulic dam in the world, in the upper Yangtze River further motivated new research considering the impact on the river systems downstream. Located in the middle Yangtze River are the Poyang and the Dongting Lakes, which are the largest (3,960 k㎡) and second largest (2,740 k㎡) freshwater lakes, respectively, in China. The middle Yangtze River system is thus characterized by complex hydrological interactions between the river and the adjoining lakes, in a manner that is regarded as unique in the world.

The exchange relationships of water, sediments, dissolved constituents and energy between rivers and lakes significantly influence the geomorphology, water regime, water quality, and aquatic and riparian ecosystems of river-lake systems. However, the operation of TGD substantially altered river-lake interactions during the past decade, and subsequently affected the water balance, water quality and ecology of the connected lakes. Therefore, the middle Yangtze River provides an ideal example to investigate the impacts of human activities on the river systems.

Considering the wide interests of this topic worldwide, a special issue of Hydrology Research on advances in studies on middle Yangtze River was composed. Although exemplified by the middle Yangtze River, the research outcomes are of significant relevance to other large river-lake systems in the world. The 20 papers included in this special issue is part of the research outcomes, and readers are encouraged to refer to publications cited in papers in this issue.

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