What Lives Below and What Flows Through: First Findings from JDS5
The ICPDR’s 5th Joint Danube Survey (JDS5) is pushing the boundaries of what river science can do. And the first preliminary results are beginning to reveal a rich and complex picture of one of the world's most studied rivers.
Chemicals in the Danube: A Record-Breaking Investigation
The number of chemicals in everyday use has grown dramatically in recent decades. Many of these substances enter rivers through households, agriculture and industry, yet a significant share remains neither regularly monitored nor covered by existing legislation. The ICPDR’s JDS5 is addressing this gap head-on.
For the first time in the history of the Joint Danube Survey, over 94,000 chemical parameters, including around 2,900 targeted substances, are being analysed using cutting-edge analytical methods. This makes JDS5 the most comprehensive chemical investigation of a river basin ever undertaken worldwide.
The leap forward is made possible by modern screening techniques that go far beyond traditional targeted analysis. Where laboratories once could only search for substances already known to be present, today's methods allow thousands of previously undetected chemicals to be identified in a single aanalysis – oftenlong before they appear in routine monitoring programmes.
However, detecting a substance does not automatically mean it poses a risk to people or the environment. That is why the JDS5 chemical results are being evaluated alongside information on their toxicity to water fauna and flora and human health; environmental fate; frequency of occurrence; and potential adverse impacts, in order to identify which substances may be of particular relevance for the future protection of the Danube.
The NORMAN Network
In JDS5, chemical investigations are carried out in partnership with the NORMAN Network, a leading platform linking research, monitoring, and policy on emerging substances with more than 100 member organisations in Europe, North America, Asia and Australia. Through its long-standing collaboration with the ICPDR within the framework of the Joint Danube Surveys, NORMAN has been supporting the harmonisation of analytical methods and enables the sharing and comparison of data across countries and programmes.
The data generated directly feed into European Commission databases, supporting the further development of EU chemicals and water policy as well as future monitoring programmes. The analysis of the data is set to be completed over the course of summer 2025.
Life on the Riverbed: More Species Than Ever Recorded
Alongside the chemical investigations, the ICPDR’s JDS5 has been exploring life at the bottom of the Danube, here too, revealing equally groundbreaking findings.
Macrozoobenthos, the invertebrate animals living on the riverbed, including crustaceans, insect larvae, worms, snails, and mussels, are among the most sensitive indicators of ecological river health. Because they respond quickly to changes in water quality and habitat conditions, they can reveal aspects of the river health that chemical analyses alone may miss.
JDS5 has recorded more than 500 different species of macrozoobenthos along the Danube. This is the highest number ever documented in any Joint Danube Survey.
One of the most striking findings is the disproportionately high contribution of rare microhabitats to overall biodiversity. Areas with deadwood or isolated aquatic plants, often overlooked in broader assessments, are proving to be unexpectedly important refuges for a wide range of species.
The data also point to broader improvements in water quality along the Danube, which is an encouraging sign. However, the picture is not entirely positive. Good water quality alone does not guarantee good ecological status required by the EU Water Framework Directive. River engineering, channelisation, and the spread of invasive species continue to put pressure on aquatic communities, and in these areas, significant challenges remain.
Looking Ahead
Together, the chemical and biological findings from JDS5 are building a detailed and nuanced picture of the Danube River and its tributaries. They highlight where progress has been made, where challenges persist, and where future efforts need to focus. Full results will be published in the official JDS5 reports in early 2027.
