Water quality

Explanation of the problem

During prolonged heat periods, the temperature of surface water rises. This leads to the growth of algae (blue-green algae) and the proliferation of other pathogenic organisms. Warmer water contains less oxygen and enhances decomposition processes in the water bottom. Shallow waterways, in particular, can warm up quickly. This makes the water more nutrient-rich and oxygen-deprived, with negative consequences for the ecosystem, such as fish mortality. It can also lead to unpleasant odours. If it is simultaneously dry for an extended period, a lower water level can increase the concentration of unwanted substances and drug residues, lowering water quality. In dry periods, it is a significant challenge to get enough clean water to the right places.

The decline in water quality is particularly a concern for municipalities and water authorities, as well as users of surface water such as agriculture, fisheries, and recreational activities. If heat (and drought) leads to salinization, locks and barriers can be closed, hindering navigation.

Information and maps for better understanding

Basic maps according to the standardized stress test


Additional maps

  • Map with the risk of warm surface water (Climate Impact Atlas) → provides insight into the locations where heat can have adverse effects on water quality and ecology.
  • Map showing the number of summer or tropical days now and in the future (Climate Impact Atlas) → provides insight into the increase in the number of days when surface water is warmed.
  • Locations of surface water → provides insight into the (critical) locations where water quality may be a problem.
  • Overview of official and unofficial swimming locations in the municipality.

Some measures and guidelines

  • Check water quality.
  • Timely warnings about the quality of swimming locations or closing swimming water locations.
  • Design urban water to make the water system more robust:
      • By designing enough shallow surface (between 0- and 1-meter depth) with plants that make the system more resistant to algae growth and bring oxygen into the water.
      • By ensuring that as little nutrient-rich (dirty) water as possible enters the system, by detecting faulty connections, preventing sewer overflows, and (re)locating rainwater outlets and sewer overflows at strategic locations in the water system.
  • Keep large water bodies sufficiently deep through dredging.