The pond water has turned green.
This is caused by algae; it can be a problem if tadpoles are in the pond as the water becomes deoxygenated.
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.
Should I top up my pond in hot weather?
Most ponds will tolerate natural fluctuations in water levels though some small ponds may benefit.
During warm weather it is natural for the level of water in a pond to drop. Most of the ponds inhabitants can tolerate these fluctuations but in very small ponds it can be a problem, especially if there are tadpoles present.
In these situations it’s best to use rain water, if it is available. If not, tap water is usually ok in small doses. Make sure it is left to stand for at least 24hrs to allow the chemicals to settle out and for the temperature to adjust – adding large volumes of water that is a different temperature can shock the pond. Tap water may also encourage algae to grow (turning the water green) so keep an eye on this.
It has been suggested that the recent use of chloramines, rather than chlorine, by water companies could be extremely harmful to amphibians as they persist in the water longer – i.e. will not have settled out after 24hrs. This is another reason why tap water should be avoided, if possible. There are products available to buy that will remove chloramines from water and make it safe.
In larger ponds there may be no need for topping up but make sure there are still exit routes for emerging amphibians and add some ‘frog ladders’ if necessary, e.g. planks of wood, a length of pipe or plants.
If a pond is seriously at risk of drying out, consider removing some silt to deepen it at the appropriate time of year.
A pond has completely dried up, should anything be done?
It depends on the time of year and the circumstances.
Amphibian ponds that dry up once in a while are actually beneficial as they ensure the pond remains free of fish. If you’re aware of a wild pond that dries up every now and again this is nothing to worry about – it may affect the amphibian population that year but should not have any long term impact.
However, a pond that has become silted-up, and is unlikely to re-fill on its own is a problem and requires some maintenance. Ideally the pond needs to be restored so that it will hold water and continue to benefit local wildlife. If this is a public pond (on a nature reserve or owned by the council) then there may be funds available to groups wanting to carry out the work – search for community or environmental funding on the internet.
How do I protect the creatures in my pond during icy weather?
Clear snow from the ice to ensure light can still enter the water, therefore allowing plants to continue producing oxygen. If you’re able, you can make a hole in the ice but this may not make any difference.
Frogs, and sometimes newts, may lie dormant at the bottom of ponds in winter. Occasionally, in particularly icy spells, frogs can die of ‘winterkill’, where toxic gases (released in the pond through natural decomposition of dead leaves) can not escape from the pond due to the layer of ice and the water can be become deoxygenated. Though this can be upsetting to pond-owners this phenomenon is largely natural and will only affect a very small percentage of the local frog population.
In your garden pond you can try and reduce the likelihood of winterkill by trying to maintain oxygen levels in the pond. Clear any fallen snow from the ice to ensure that plants can still produce oxygen. It’s also a good idea to prepare your pond for winter by removing some sediment and debris (though leave some for the frogs to bury down in) and adding more oxygenating plants if necessary. If you have a pump, it’s a good idea to leave this running over the winter.
It will not do any harm to make a hole in the ice, if you choose to do so, and it can be beneficial for fish and other creatures. The best way to do this is to leave a ball or other floating object in the pond which can be removed to leave a hole after it freezes. Alternatively you could use a pan of hot water placed on the ice to melt a hole. Never pour hot water onto the ice or use chemicals or salt. Similarly, do not be tempted to smash the ice as this can damage the pond liner and the pond life.
If you find any dead frogs, you can register them with the Garden Wildlife Health project.