Q&A on the Water Main Break in Amsterdam-Noord

The discharge of wastewater has caused contaminated particles and sediment to become visible. In addition, dark flakes may form due to oxygen depletion and natural decomposition processes. At many locations, these phenomena are now subsiding. In some places, small pieces of peat are floating to the surface due to gas formation. 

If you notice water grey , floating flakes, or other unusual phenomena in the water, please continue to report them so that we can keep monitoring the situation. It is important that you provide the location as accurately as possible. Reports can be submitted during office hours (8:00 a.m. – 5:00 p.m.) by calling 072-582-82-82 and outside office hours by calling 0800-1430. 

The discharge of sewage has introduced additional nutrients into the water. This triggers various natural processes in the water. Among other things, these processes can produce a gas that smells like rotten eggs. As a result, this odor may be noticeable in the area for a short time. 

The fish die-off was caused by a lack of oxygen. This was the result of a combination of hot weather, naturally low oxygen levels in the water system, and the large amount of nutrients from wastewater. As a result, microorganisms consumed virtually all the available oxygen in the water.

At this time, no new reports of dead fish or fish in distress have been received. However, the situation is being actively monitored. If you see dead fish or fish gasping for air at the water’s surface, please call us during office hours (8:00 a.m.–5:00 p.m.) at 072-582-82-82 and after hours at 0800-1430. Please provide the specific location where you saw these fish.

HHNK and Waternet jointly began removing the dead fish on Wednesday, September 2. In the days leading up to that, the extent of the pollution was not yet fully clear. Based on reports of dead fish and the measurements taken, it became clear on Monday, August 31, and Tuesday, September 1, that the situation was more serious and widespread than initially assumed. 

In hindsight, the cleanup of the dead fish could have been started sooner. Initially, it was expected that the wastewater would be significantly diluted by the heavy rainfall and that the consequences would be limited. It later turned out that the extent of the pollution was greater than anticipated. This point will be included in the evaluation.

No exact figures are available on this. The effort was focused on removing dead fish as quickly as possible and limiting further negative effects on the aquatic ecosystem.

Due to a break in the pressure pipe, sewage has entered the surface water. Therefore, the recommendation is not to use the surface water in the affected area.

It is always a good idea to check the current swimming advisory for a particular swimming location. The province is responsible for ensuring the safety of swimming waters and, based on the water quality data it receives, may issue a negative swimming advisory or a swimming ban for official open-water swimming locations. For more information, visit www.zwemwater.nl  

To do so, please contact the GGD. 

In that case, follow the usual hygiene measures: rinse your skin or the materials with clean water and soap, and watch for any health symptoms. If you experience any health symptoms, contact your family doctor.

The advisory will remain in effect until measurements show that water quality has sufficiently recovered. As soon as more information is available, it will be published at www.hhnk.nl/persleidingbreuk.  

The placement of warning signs is being evaluated in consultation with the GGD.

Surface water poses risks. Its quality can change rapidly due to hot weather (such as blue-green algae or bacteria) or due to discharges. HHNK and the Union of Water Boards generally advise against using untreated surface water as a water source for animals, because, unfortunately, the water quality is generally poor. The introduction of large quantities of municipal wastewater into a water system—such as that caused by this pressure pipe rupture—reinforces this recommendation.

If your pet is showing signs of illness, we recommend that you consult a veterinarian.

Surface water poses risks. Its quality can change rapidly due to hot weather (such as blue-green algae or bacteria) or due to discharges. HHNK and the Union of Water Boards generally advise against using untreated surface water as a water source for animals, because, unfortunately, the water quality is generally poor. The introduction of large quantities of municipal wastewater into a water system—such as that caused by this pressure pipe rupture—reinforces this recommendation.

We fully understand that information is being requested at the local level. The sampling results are being analyzed, but we are asking GD-Diergezondheid—a Dutch company based in Deventer that is dedicated to the health of farm animals and companion animals—to assess whether there are any restrictions on livestock grazing. We adopted this suggestion based on feedback received during the residents’ meeting on September 10.

Surface water may naturally contain contaminants and may therefore pose risks. Water quality can vary due to factors such as weather conditions, runoff, bacteria, algae, or other contaminants. For this reason, we generally recommend exercising caution when using untreated surface water for irrigation.

In addition, a large amount of municipal wastewater entered the water system as a result of the pressure pipe rupture. Therefore, it is not recommended to use surface water from the affected area.

According to the GGD, food products that have been sprayed with contaminated surface water may have become contaminated. The recommendation is to wash fruits and vegetables thoroughly, peel them when possible, and cook them thoroughly before eating. These are general hygiene measures that also apply to the regular use of surface water, since surface water can naturally contain contaminants. 

Rainwater is the very best, so we always recommend it. 

No, the current recommendation is not to dredge ditches in the affected area. This also applies to cleaning the ditches. First, it must be determined whether and to what extent the waterbed has been contaminated as a result of the pressure pipe rupture. Investigations into this matter are still ongoing. More clarity on this issue is expected by the end of September.

Until that clarity is established, we recommend that no dredging operations be carried out in the affected area. As soon as the results of the investigation are available and the recommendation is updated, we will provide an update via hhnk.nl/persleidingbreuk.

Yes. Mowing and cleaning ditches through dredging are two different activities. Mowing can continue. As for cleaning ditches, the current recommendation is to wait until there is more clarity regarding any contamination of the riverbed. 

No, the recommendation is not to clean the ditches in the affected area. First, we need clarity regarding any potential contamination in the soil. We expect to be able to provide clarity on this by the end of September. The inspection has been postponed. You may disregard the letter regarding the fall inspection for now. When the above recommendation is lifted, we will provide an update via www.hhnk.nl/persleidingbreuk.  

A diversion route was immediately set up to divert wastewater. In addition, measures taken included installing aerators, using pumps to supply cleaner water, draining contaminated water, removing dead fish, and conducting additional water quality tests.

To increase the oxygen content in the water, aeration pumps have been installed at several strategic locations. In addition, extra pumps are being used to bring in cleaner water and further dilute the contaminated water. 

The peak pollution was discharged via the Kadoelen pumping station. Now, the water is discharged via the Kadoelen pumping station into the North Sea Canal or via the De Poel pumping station into Lake Markermeer. 

No. Waternet is working on the repair. It is expected to take at least two weeks. 

Repairing a pressure pipeline of this size is technically complex. Waternet is working day and night on the repairs. At the same time, wastewater discharge must continue to be ensured via a temporary diversion route. For this reason, the repairs are expected to take at least two weeks. 

At this time, there is no danger to the surrounding area from the pressure pipe. 

Various scenarios have been developed to address changes in weather conditions. The organizations involved are closely monitoring the situation and will take additional measures as necessary. 

Water quality has been monitored at fixed monitoring points in the area for many years. The attached map shows these monitoring points. Due to the pipe break, samples are being collected at these fixed monitoring points in the area to determine the impact of the break. This allows us not only to assess the current situation but also to compare it with previous monitoring data from the area.

As soon as all the measurements have been received and analyzed, the results will be made public. 

The additional sampling began on September 7, 2026. Initial results are expected during the week of September 21–25, 2026.

We will continue to monitor the oxygen levels until they stabilize and reach the correct level.

Sampling is performed by an accredited laboratory with expertise in aquatic sediments and surface water.

Yes, ecological impacts are part of the monitoring process. An ecologist is involved in the study. It is still too early to draw conclusions.

Water quality testing is intended to provide insight into the presence of substances that have entered the water system via municipal wastewater. The final results are not yet available.

An investigation has been commissioned to assess the quality of the riverbed. In addition, samples are being collected at existing WFD monitoring sites to assess the impact of the pressure pipeline rupture on water quality and the riverbed. The results will be used to identify any potential impacts and determine whether additional measures are needed.

That is not yet known at this time. A study has been commissioned to assess the quality of the riverbed. Sampling is taking place primarily in the vicinity of the pressure pipe rupture and is being conducted by an external firm.
 

If the investigation reveals that the waterbed has been contaminated as a result of the pressure pipe rupture, HHNK will hold the party responsible—in this case, Waternet—accountable for cleaning up the contamination. The necessary measures will be determined based on the results of the investigation.

The cause is not yet known. Waternet is investigating the cause of the pipe break. The results will be made public at a later date.

This is part of the evaluation. Waternet is investigating whether the pipeline could have been shut off more quickly and what lessons can be learned for the future.

The spread of the contaminated water was caused by a combination of factors. After the pressure pipe ruptured, a large volume of wastewater entered a vast and complex water system, in which water levels, flow directions, and discharge capacity vary by area. 

Initially, the decision was made to discharge the contaminated water via the Kadoelen pumping station toward the North Sea Canal. The wind was favorable for this. The Kadoelen pumping station was activated, and the De Poel pumping station was deactivated. At that time, it was expected that the wastewater had been significantly diluted by the heavy rainfall and that the impact on the water system would be limited. Furthermore, damming off such a large volume of contaminated surface water is not feasible, and the water had already penetrated further into the system.

In the days that followed, the situation continued to develop. The wind shifted direction and picked up in strength. At that point, it was no longer possible to discharge the water via Kadoelen. The decision was made to discharge it via De Poel instead. We let water in at Kadoelen. There was a lot of rain, which helped dilute the contaminated water further. 

Yes. We want to commission an external investigation into how Waternet and HHNK handled the pipe break. That investigation will begin once we have completed the phase of implementing measures and making repairs. We expect that to be in November. We will define the scope of the investigation in consultation with the advisory group.

That is part of the investigation and evaluation. Among other things, the investigation will examine the cause of the pipe break, the detection of incidents, and the response during the emergency.

Yes. The results of the evaluation will be shared via www.hhnk.nl/persleidingbreuk. 

Yes. A focus group is being formed with residents and other stakeholders from the area to draw on local knowledge and contribute ideas regarding restoration, monitoring, and next steps. An invitation has already been sent to the focus group for an initial meeting.