The Fischa rises in the Steinfeld near Haschendorf in the municipality of Ebenfurth, flows through eleven municipalities in the southern Vienna Basin and flows into the Danube at Maria Ellend. It is 35 km long, the difference in altitude is very small at 86 m. Its catchment area is 563.1 km². The source is located on the eastern edge of the Piestinger gravel fan (also called Wöllersdorfer Schuttkegel) and the Fischa drains it. It is a flowing waterbody almost exclusively characterized by groundwater supply, therefore it has a very stable water level and a rather constant water temperature. At Gramatneusiedl the Piesting flows into the Fischa.
Fischa Kleine Au
In the local area of Fischamend, the Fischa river splits into three arms. Fish passability in this section was restored in the area of the right arm at the dividing spur by constructing an asymmetrical ramp.
In spring 2021, the fish ladder on the Fischa in the Kleine Au of the municipality of Fischamend was completed. In combination with the revitalization of the Fischa mouth, this measure serves to improve the passability of the Fischa and, above all, the spawning situation for ascending fish from the Danube.
In order to be able to measure the potential of these species to travel upstream and thus also the functionality of the fish passage, monitoring was established at the beginning of spring and a control trap was set up at the upper end of the fish passage. This trap is used to catch the specimens that ascend via the fish ladder. The fish trap is emptied daily to count and measure the fish. They are then gently released back into the water.
After more than 100 days of fish trap monitoring, the first positive results can be drawn. To date, 21 species of fish have found their way up the ladder - including all the leading species typical for the waterbody. Furthermore, during the spawning season in spring, spawning fish could be captured by fish traps, i.e. the situation for the spawning migration of Danube fish has already improved due to the installation. Unfortunately, the total number of documented fish was not in the desired range. This may be due to several factors. For example, in 2022 extreme drought caused long-term low water levels in the Fischa River, which also affects the biomass of upstream fish. In order to assess the long-term effect of the measure, it is therefore important to continue the monitoring program over the next years.
The objectives of this revitalization were the restoration of river, riparian and bank structures typical for the site as well as fish ecological improvements in the area where the Fischa flows into the Danube. The hard bank obstruction was mitigated at the end of 2019. Upstream of the river mouth, the obstruction was lowered over a length of 125 m, and downstream about 130 m of block stones were completely removed.
In a further revitalization step in the fall of 2020, the level of the hinterland above the mouth was lowered to create a shallow side arm with a temporary downstream connection to the Fischa River. The affected area used to be a water area and was backfilled in the course of the then usual maintenance activities of the waterway. The Danube gravel now present there, was removed and the material was returned to the bedload cycle of the Danube.
A habitat was created that significantly improves water connectivity, providing aquatic and semi-aquatic habitats, particularly for juvenile fish and amphibians, as well as macrozoobenthos and waterfowl. In addition, reduced gravel thickness will promote the emergence of vegetation typical for the site.
Together with the restoration of passability in the Kleine Au near Fischamend, the habitat situation for many aquatic species in the Fischa has already improved considerably shortly after completion.