A cyanobacterial bloom - what to do and how to prevent it
In summer, a greenish “scum” on the water and streaks by the bank are often a cyanobacterial bloom - a phenomenon that can threaten the health of people and animals, because cyanobacteria produce toxins. It is worth knowing what to do in the moment and how to reduce the risk over the longer term.
An informational article. On matters of bathing sites and safety, follow the announcements of the services (including the sanitary inspectorate) and local managers.
How to recognise it
- a green/blue-green scum or streaks, water like “pea soup”, an unpleasant smell,
- a sharp fall in transparency (see the Secchi disc),
- it is favoured by warm, calm, sunny weather and fertile water - see bloom monitoring.
What to do in the moment
- Limit contact - do not bathe and do not let animals bathe in water with a bloom; do not drink or use it without treatment.
- At a bathing site - follow the announcements and bathing bans; report a noticed bloom to the manager.
- In a pond - aeration and improving the mixing of the water can help; avoid “miracle” chemicals without consultation (they can make the situation worse, e.g. by releasing toxins).
- Observe - a bloom can move (wind); note and document it.
How to prevent it in the long term
Cyanobacteria are driven by an excess of nutrients, so the key is limiting the inflow of nutrients:
- less fertilisation and run-off from fields, efficient sewage management,
- strips of vegetation along the banks (a buffer), protection of the catchment,
- in water bodies - measures limiting the release of phosphorus from sediments.
This is a fight with the cause (eutrophication), not just with the symptom.
In practice
Early detection gives an advantage. Systematic monitoring of transparency, chlorophyll and weather lets you anticipate the risk. In LimnoLog you can keep these indicators together (with weather from connectors), and share the current picture via a public link - e.g. with a bathing-site community.
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