The paper presents a study on the retention ditch system characterised by varying hydraulic and geometric parameters, especially longitudinal slopes as well as dimensions and cross-sectional profiles. During the pre- modernisation inventory of the site, only one concrete structure was found on the R-E ditch, with fixed, circular outlet openings. The existing weir height provided a dead retention capacity of 2% geometric capacity of all ditches in the system, and a usable capacity of 23%. It allowed to use only 25% of the full geometric capacity, without water level control.
As part of the modernisation, the existing concrete structure was removed, and replaced by seven new damming structures, including three structures on the R-E and R-E1 ditches and one on the R-E4 ditch. These were four plastic structure weirs with movable closures that allowed to regulate the water level, two permanent crest weirs and a disc regulator built into the culvert pipe. These changes reduced the dead storage volume to 1%, and increased the usable storage to 41% of the geometric storage of all ditches in the system. This ensured 42% utilisation of the geometric capacity. The increased water damming in indicated places, it was possible to use the geometric capacity of the ditches up to 65%.

The European eel (Anguilla anguilla) is a catadromous fish with a complicated life cycle. The long-term impact of anthropopressure, environmental pollution and diseases have led to a risk of extinction. The aim of the present study was to determine the influence of Anguillid herpesvirus-1 infection on the innate immunity of European eel from natural conditions. Spleen phagocyte respiratory burst activity and potential killing activity, as well as pronephros lymphocyte proliferation stimulated by concanavalin A or lipopolysaccharide were measured. The analyses of the results showed that all studied parameters were significantly higher (P<0.05) in AngHV-1-negative fish compared to the ones where the presence of viral DNA was confirmed.