Neither Crayfish Nor Water

MAGYARUL

however in principle, both would be required to name an old branch of the Danube in Vienna Krebsenwasser. If neither exists anymore, it might be better to call it Unteres Heustadlwasser, as these two bodies of water formed a common riverbed in the Prater before the great Danube regulation. 

What is this all about? There is a world of difference between the appearance of the Danube in Vienna before and after 1875. Until the river was regulated, the Vienna section of the river was constantly changing and and transforming landscape, very conducive to the formation of islands and gravel bars, where no distinct main channel could develop, where the Viennese had to fight a constant battle with the river, which changed its course from year to year, and where communication between the right and left banks was rather difficult. The ancestor of the Krebsenwasser, the Heustadl-Danube, was once a main branch of the Vienna Danube, which began to migrate towards the right bank, the city, in the early 1600s, reaching its greatest width at the beginning of the 18th century. Its meandering broke through the tree-lined avenue leading to the Lusthaus and between 1704 and 1713 threatened to break through into the Vienna branch, which was the predecessor of today's Donaukanal. This catastrophe was averted by closing the Heustadl-Danube, but as a result, this branch gradually withered away during the century and was only one of many tributaries when it was finally closed off from the main branch in 1875. 

The separation of the Krebsenwasser and the Heustadlwasser after 1875. (mapire.eu)

A total of four former branches of the Danube remained in Vienna's Prater after the radical river regulation intervention of 1875, when one of the largest island destruction in the history of the Danube took place. Of the remaining branches, we have already visited the Lusthauswasser and the upper branch of the Heustadlwasser. The elimination of the Viennese archipelago with a single straight channel allowed the city to begin its expansion into the floodplain areas at the expense of the Danube's labyrinth of riverbeds, shoals, and islands. 

Where are we, what do we see? The shrinking Hesutadlwasser and the Vienna Prater. (source)

Since the Prater has long functioned as Vienna's city park, development here has been largely restricted by nature conservation considerations, and certain open water sections have been preserved, but one of Europe's busiest transport routes, the eight-lane A23 motorway, was nevertheless built here in 1978.

The lower part of the Prater and the new section of the Donaukanal. (source)

As far as the motorway is concerned, at least they took into account that it was built as a bridge over the dense, wooded area, but it is still not the classic canopy walkway that would normally be built in such a place. Due to lack of space in Vienna and other large cities, infrastructure investments are often constructed at the expense of remaining natural habitats, such as in the case of the new Vienna transport corridor planned through the Lobau floodplain on the left bank. If we look only at the Krebsenwasser without the Upper Heustadlwasser, here too two roads have further fragmented the remaining Danube backwater. The first is the Aspernallee, which runs from the Praterkai railway station to the east of the Haustadlwasser and Krebsenwasser break, arriving at the Lusthaus' star from the northeast. Road traffic runs along this road, and a narrow culvert at the intersection provides a connection between the two parts of the riverbed. To the east of the Maria Grün Catholic Church, which is used by Croatians living in Vienna, a narrow embankment leads across the riverbed, under which there is also a culvert built of concrete rings, but on this road only a forest path used by hikers leads to Dammhaufengasse. In addition, another path crosses the riverbed where the forest opens up slightly and gives way to reeds, indicating that the time has not yet come for woody plants to take over this depression.

The Krebsenwasser from the Aspernallee.

Embankment across the old riverbed, towards the Dammhaufengasse.

The remaining treeless riverbed.

The Krebsenwasser in morning sunshine, across.

The Krebsenwasser in morning sunshine, along.

The remaining water with an out-of-order gauge.

The esastern end of the Krebsenwasser.

The living and the dead.

On October 28, 2025, there was only a little water in the deepest part of the Krebsenwasser, mostly hidden from curious eyes by reeds. Hopefully, if there are any remaining specimens of the eponymous crayfish, they can hide here, waiting for rainier times. The only water gauge in the 30-meter-wide and 300-meter-long section of the riverbed was dry at this time. 

In the wooded section towards Aspernallee, the morphology of the riverbed was recognizable, but its vegetation was no different from that of the surrounding, higher-lying forest areas. The soil was somewhat softer and wetter, but there was no sign of surface water, nor was there anything to suggest its presence. The deeper part of the Krebsenwasser is probably only replenished by groundwater and precipitation, which can be sucked up through the gravel bed by the low water level of the current main branch flowing just 200 meters away.

The water shortage, drying up of backwaters, and reforestation observed in the case of Krebsenwasser can be seen not only in the Prater, but also in the Lobau area on the opposite bank. This is a natural process (after the anthropogenic Danube regulation), as in the absence of water flow (flooding in the Prater is practically impossible nowadays), dust, leaves, rubbish, etc. that fall into the water cannot be washed away. However, this process can be faster or slower, depending on the precipitation and groundwater conditions in the area. The year 2025 will go down in hydrological history due to its exceptionally low water levels, and this situation is also reflected in the case of Krebsenwasser during the autumn low water period.

Here, too, there is nothing left to do but to document the final drying up. 

Translated with DeepL.com (free version)