FAQs about ponds: algae

Algae can be a problem if persistant (Natalie Giles)

WILDLIFE INFORMATION SERVICE

Frequently Asked Questions about... ponds:

The pond water has turned green with algae, is this a problem and, if so, how do I solve it?

Green water is caused by algae (microscopic plants) which can cause problems for other pond life by blocking out sunlight and using up vital nutrients. Although some algae is beneficial to the pond (tadpoles feed on it), a sudden algal bloom can be devastating.

Algal blooms are more common in new ponds and will often clear naturally once the pond has settled in. In more established ponds the causes can be too much sunlight or an excess of nutrients (e.g. from the use of fertilisers on surrounding land).

In the long term, a healthy pond should be able to avoid persistent algal blooms by maintaining the right balance of plants (which will use up available nutrients, block out a little sunlight and provide plenty of oxygen). If you are keen to treat the problem then adding silt from a nearby pond may help as it will contain insects like water fleas (Daphnia) which will feed on the algae; if this is not possible then Daphnia can be purchased from many aquatics/garden centres.

Another option is to use barley straw or barley straw extract. There is still a lot of debate over how effective this is but it is probably worth a try. Do not treat the water with any chemicals or pond tonics, even those that claim to be wildlife friendly can disrupt the natural balance of the pond and cause more problems than they solve; they may also be only a temporary solution.

More information:

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