Climate change poses new challenges for reservoir management and aquatic ecology

Weather extremes are no longer the exception, but are increasingly characterising the "new normal". "For the Ruhrverband and the AWWR, this means a constantly growing challenge in terms of reservoir management and safeguarding water quality for the region," emphasised Prof. Christoph Donner, Chairman of the Ruhrverband Executive Board, and Bernd Heinz, Chairman of the Arbeitsgemeinschaft der Wasserwerke an der Ruhr (AWWR), at the joint presentation of the 52nd edition of the Ruhr Quality Report on 30 September 2025 in Essen. edition of the Ruhr Quality Report on 30 September 2025 in Essen. 

Extreme years in a row 
The year 2024 set several records: for the third time in a row, the average annual temperature was above 10 °C - a value that had never been reached since records began in 1881. At the same time, 2024 was one of the five wettest runoff years with 30 per cent more precipitation than the long-term average. At the beginning of 2024, there was also an unusually long flood phase lasting almost two weeks. 2025, on the other hand, presents a completely different picture: a precipitation deficit of almost 40 per cent since February and the driest March in over 30 years in the Ruhre catchment area led to an exceptionally early obligation to make contributions from the dams. At 169 days, the duration of the subsidy significantly exceeded the figure for the entire previous year (64 days). 

Amendment to the law strengthens security of supply 
The amendment to the Ruhr Association Act in December 2024 lowered the minimum water flow limits by 3 m³/s. Since its first application on 1 July 2025, this has saved around 22 million cubic metres of water - almost twice the storage volume of the Ennepetalsperre dam. "Even after a short time, it is clear that this adjustment has significantly increased the security of supply for 4.6 million people," emphasises Prof Christoph Donner, CEO of the Ruhrverband.

Focus on ecological changes 
Water ecology is also changing rapidly. The invasive aquatic plant Elodea, which displaces native species, showed pleasingly weak growth in 2025: in Lake Baldeney, only 9 tonnes were mowed instead of 510 tonnes in the previous year. Nevertheless, the personnel and financial costs involved in combating it remain high. At the same time, the water temperatures of the Ruhr are rising: by 1.9 °C since 1985 and by as much as 2.1 °C in the winter months. The consequences are increased oxygen consumption, poorer mixing of the reservoirs and oxygen deficiency in deeper layers. Added to this are serious pressures in rivers and streams due to changing discharges, low water phases and even droughts and floods, which reduce habitats and push back native species such as brown trout and grayling. In contrast, warmth-loving and invasive species such as gobies are spreading. 

Progress in nutrient elimination - new challenges posed by trace substances 
Since 1970, the nutrient load in the Ruhr has been massively reduced: Ammonium nitrogen by 96 per cent, phosphorus by 91 per cent. However, in order to maintain this level, high reinvestments in wastewater treatment plants are necessary. At the same time, the accompanying agreement to the amendment of the Ruhr Association Act and the new European Municipal Wastewater Directive (KARL) require additional measures to eliminate trace substances, such as the reduction of diclofenac. Although KARL provides for 80 per cent cost sharing by manufacturers, the pharmaceutical associations in particular are opposed to this regulation. If the polluter pays principle is not implemented, there is a threat of double-digit percentage increases in wastewater charges for the population (source: BDEW, Die Erweiterte Herstellerverantwortung in der kommunalen Abwasserrichtlinie (2024/3019/EU): ein umweltökonomischer Meilenstein).

Powdered activated carbon dosing systems have already been in operation at two wastewater treatment plants since June 2025 due to the adjustment of the minimum water flow, which successfully reduce diclofenac. However, the Ruhrverband is also calling on citizens to do their bit: "Anyone who avoids painkillers containing Diclofenac and instead seeks medical advice is actively protecting our waters."

Outlook 
Climate change is profoundly altering the framework conditions for water management and aquatic ecology. The Ruhrverband believes it has a responsibility to ensure security of supply. "But solutions for a climate-resilient future can only be developed together with politicians, industry and the population. The ecological targets for implementing the Water Framework Directive must also be adapted to the new realities," demands Prof Christoph Donner.

Arbeitsgemeinschaft der Wasserwerke an der Ruhr (AWWR) 
The 18 member companies of the Arbeitsgemeinschaft der Wasserwerke an der Ruhr e.V. (AWWR) ensure that around 4.6 million people, businesses and industry along the Ruhr are always supplied with sufficient quantities of drinking water of impeccable quality. The NRW water strategy currently being drawn up by the state opens up the opportunity to implement the necessary and innovative concepts and measures for a continued future-proof water supply in the Ruhr catchment area.

Water quantity management and quality
From July this year, the Ruhrverband was able to implement the new low water management system in good time to protect the reservoir levels. The AWWR expressly supports this in order to be able to cope with long dry periods without supply restrictions.

In terms of quality, there were no significant anomalies in raw and drinking water in 2024, a year with plenty of water, nor in the year with little precipitation to date. Nevertheless, quality monitoring is being further expanded and intensified using modern methods. In addition, the construction of the last two large drinking water treatment plants in the AWWR area in Halingen and Warmen is progressing according to plan. "We have now achieved a secure volume supply in the Ruhr as climate change progresses. The focus is now on quality aspects and resilience measures," says AWWR Chairman Bernd Heinz.

Water suppliers are faced with the challenge of having to take into account a growing number of legal requirements and administrative processes. From the perspective of AWWR members, only limited progress has been made to date on fundamental issues and the implementation of measures to secure the drinking water supply in NRW in the long term. For example, the flood protection measures following the heavy rainfall event in July 2021 are only developing gradually, supra-regional supply approaches require longer planning periods and approval procedures are often complex and lengthy.

NRW water strategy 
The NRW Ministry of the Environment will draw up an NRW water strategy by the end of the year with the involvement of water suppliers. "An ambitious NRW water strategy must set out the guidelines for a future-proof drinking water supply and implement these with concrete and innovative measures," says Bernd Heinz. 

The adaptation of the low water management system on the Ruhr took a total of six years from the initial findings at the end of 2018 to legal implementation in a complex and time-consuming process. Fortunately, water shortages on the Ruhr have been avoided in the meantime. 

This case shows that we will have to make adjustments to the changed situation much more quickly and pragmatically in future. In addition to the consequences of climate change such as drought and flooding, quality aspects, safety issues and energy supply are also at the centre of attention. Drinking water from the Ruhr is the basis of life for the people and economy of the region.

The new NRW water strategy is therefore an opportunity to create feasible elements for flood protection, network expansion with supra-local supply as well as consistent digitalisation and transparency in addition to water-related aspects relating to water quantity/quality and the environment. In addition, financing issues for the additional measures need to be resolved. Bernd Heinz comments: "We expect the NRW water strategy to take bold steps to speed up processes, reduce bureaucratic hurdles and ensure practical implementation, as otherwise many future-oriented projects on the Ruhr will only be realisable to a limited extent or not at all under the current framework conditions." AWWR members are happy to make concrete suggestions to increase the speed of implementation.

Background information AWWR
The Arbeitsgemeinschaft der Wasserwerke an der Ruhr e. V. (AWWR) has been committed to a safe drinking water supply in the Ruhr for over 75 years. It is a voluntary association of now 18 water supply companies from its source in Winterberg to its mouth in the Rhine. They supply around 4.6 million people, businesses and industry along the Ruhr and in some cases beyond with around 240 million cubic metres of drinking water per year. When it comes to water management issues in the Ruhr catchment area, the AWWR represents the interests of the river. More information at www.awwr.de. 

Link to download the Ruhr Quality Report 2024