Chemicals in Swimming Waters

According to a study (published in September 2026) by Natuur & Milieu and the Netherlands Institute of Ecology (NIOO-KNAW), chemical levels exceed the standards in virtually all swimming waters. On this page, we explain the various standards and the role of the water board, and we answer frequently asked questions.

We have requested the data used in the study from Natuur & Milieu. Once we receive it, we will review it before providing a more detailed response.

Water Quality Measurements

Every year, HHNK conducts numerous water quality measurements. These measurements are necessary for our work and for our legal obligations. We consider it undesirable for substances to be present in the water, especially if their concentrations exceed environmental standards. The research report shows that swimming waters are not closed systems. Substances from the surrounding environment can therefore end up in the swimming water. We already knew this, and this report confirms it once again.

Different standards

The report compares the measurement results with environmental standards for water quality. These standards are intended to protect plants, animals, and the aquatic environment from the harmful effects of substances. They are not designed to assess health risks to humans. When assessing health risks, factors such as the amount of water exposure, the duration of exposure, and the frequency of contact—for example, while swimming—are also taken into account. Because environmental quality standards serve a different protective purpose and are derived using a different methodology, exceedances of these standards cannot be directly translated into health risks for humans.

No PFAS exceedances

There are public health standards for PFAS. The measurements taken by HHNK in 2024 at the official swimming water sites, as commissioned by the province, show that these standards are not being exceeded in our area.

What is HHNK doing to reduce chemical substances in the water?

HHNK monitors discharges into surface waters and tracks water quality. If prohibited substances are found at levels exceeding environmental standards, we always report this to the Netherlands Food and Consumer Product Safety Authority (NVWA). We also investigate the sources of these substances. Together with other government agencies and organizations, we work on solutions to improve water quality.

Frequently asked questions

Is it safe to swim at official swimming spots?

For more information about the health risks of swimming in surface water related to chemical substances, please visit https://www.zwemwater.nl/gezondheidsrisicos/. This website also provides up-to-date swimming water advisories based on swimming water parameters such as blue-green algae and other bacteria that can cause acute health problems.

Why are the standards for plants and animals different from those for humans?

Aquatic plants and animals live in surface water continuously or for a large part of their lives. As a result, they are often exposed for long periods to substances present in the water. In addition, aquatic plants and animals are often more sensitive to the negative effects of pollutants. Environmental quality standards have therefore been established to prevent harm to plants, animals, and ecosystems even during prolonged exposure. For this reason, environmental standards are often stricter than public health standards. Humans and terrestrial animals come into contact with surface water much less frequently and for shorter periods of time. Consequently, the health standard is generally less stringent. Furthermore, humans, animals, and plants can absorb, metabolize, and excrete substances in different ways. As a result, the concentrations at which effects occur can vary by species. For this reason, environmental quality standards and health standards are based on different principles and may differ from one another.

Is it safe for my dog to swim?

Environmental standards for water are not designed to assess health risks to dogs. These standards are intended to protect plants and animals in the water. To determine whether a substance is harmful to dogs, more information is needed—such as how toxic the substance is to mammals and how much of the substance a dog ingests. Public health standards were developed for humans, not for mammals such as dogs. This is because humans and dogs differ in body structure, behaviour , and exposure to surface water. For example, dogs may ingest more water while swimming (e.g., by drinking and licking). Therefore, public health standards for humans cannot simply be used to assess risks to dogs; at most, they can serve as a preliminary indication.

What is the water board doing to ensure swimming water quality?

Together with the Stichting Waterproef laboratory, we ensure that the 31 official swimming locations in our waters are sampled monthly for swimming water parameters. These include blue-green algae, which can be toxic, and various bacteria—such as E. coli—that can cause acute health problems. In addition, water clarity, temperature, pH, and other parameters are measured. The province is the competent authority when it comes to swimming water. HHNK evaluates the measurement data and advises the province, which decides whether or not to issue a warning or a negative swimming advisory. For more information, see the Swimming Water page.