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  you are in: ADVICE > FAQs > PONDS > GREEN WATER



Advice and Resources

Frequently Asked Questions about...

Ponds


The pond water has turned green.

Quick answer
This is caused by algae; it can be a problem if tadpoles are in the pond as the water becomes deoxygenated.

Further information
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 - the water becomes deoxygenated and tadpoles die.

Algal blooms are more common in new ponds and will usually 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 - these 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 - though we're wary about recommending this as you could potentially introduce invasive plants, diseases or animals to the pond. Another option is to purchase Daphnia from an aquatics/garden centre.

One recommended treatment is 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 as it will not cause any harm even if it doesn't help. There are plenty of other treatments for algae available to buy and if you do decide to try them opt for 'natural' or 'bio active' products. These may not be an ideal solution as even wildlife-friendly products can disrupt the natural balance of the pond and cause more problems than they solve; they may also be only a temporary solution.

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