The book combines peer-reviewed versions of invited lectures and regular presentations at the 40th International School of Hydraulics, held May 23–26, 2023, in Kąty Rybackie, Poland. With contributions from world-leading experts and young researchers, many areas of environmental hydraulics are addressed here, including recent findings in numerical modelling and laboratory and field studies related to sediment and pollutant transport processes in rivers, fluvial morphodynamics, flow in vegetated channels, hydraulic structures in rivers and estuaries, and freshwater fish protection.