Blue-green algae (or cyanobacteria) occur in fresh, brackish and sea water throughout the world; in the UK they can sometimes appear in large blooms during the summer months in ponds, lakes, reservoirs and old gravel pits.
While usually green, or blue-green in colour (hence the name), they may be khaki, blue, black, dark brown or red. Blooms of blue-green algae can form thick scums on the surface of the water and are often cause for concern because as they start to break down they can release a range of toxins. If these toxins are ingested in large quantities they can present risks to human health and long-term exposure of human skin to the toxins can cause irritation. The effect on humans in the UK has been limited to illness rather than death and there are a number of steps that you can take to minimise the risk associated with blue-green algal blooms.
There are a wide variety of types of blue-green algae and the fact that each of them can behave differently means there are no strict guidelines on whether it is safe to continue using recreational waters in the event of an algal bloom. Instead, it is recommended that a risk assessment be made on a case-by-case basis to establish what is necessary to protect the health of water users.
The RYA has therefore produced a guidance note (available to download to the right of this page) for those clubs wishing to continue operating on their water if blue-green algae are present. The guidance note also contains a section of advice for those teaching children and vulnerable adults.
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