Heatwave hits UK pond owners


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Fish and invertebrates in rivers and ponds around the UK are suffering as the heatwave raises water temperatures and oxygen concentrations plummet.

Many areas have reported on the problems caused in local ponds and rivers, with the increased heat resulting in lower oxygen levels and advanced algal growth, killing many fish and invertebrates across the UK.

Hemel Today reports that experts in Hemel Hempstead are concerned at the low water levels and rising water temperatures in the local water gardens and the River Gade.

Action has been taken to move fish from the water gardens into the deeper waters of the River Gade in an attempt to save affected species. Peter Kirby told Hemel Today that several native crayfish were also noted to be in distress in the local area.

The Birmingham Post reported that a summer cleanup has been launched after at least 50 fish died in the Moor Pool in Harborne. Environment Agency Officials had to pump supplies into the water to boost oxygen levels.

The hot weather can also cause problems for pond owners due to a phenomenon known as summer fish kill. The problem is caused by low levels of dissolved oxygen in the pond water, and fish usually die early in the morning, with mainly larger fish being affected.

During hot weather water is capable of holding less dissolved oxygen than at cooler temperatures, and if there are large numbers of fish, organic wastes or aquatic plants in the pond the oxygen levels can plummet to dangerous levels.


Don't plant your ponds too heavily and instead stick to mechanical aeration and circulation if possible, rather than oxygenating plants. The reason for this is that although oxygenating plants help during the day, they consume oxygen at night making conditions in the pond even worse for the fish. Also try to keep algae under control, as it also consumes oxygen from the water during the night.

Water circulation

Water circulation is crucial in keeping down the temperature and raising oxygen levels, this means that in very hot conditions pumps and fountains must be kept on 24 hours a day.

Many fishkeepers lose their fish by switching off pumps and fountains at night so make sure yours is kept on 24 hours during the hottest periods.

Because oxygenating plants and algae produce oxygen during the day and consume oxygen at night, don't be tricked into thinking that you don't need to ensure adequate aeration just because your pond is rich in plant growth. It should help keep your fish alive by leaving the pump running all night and day, but you may end up annoying the neighbours a little!


Fishkeepers should avoiding feeding their fish heavily on the hottest days. Feeding your fish in very hot conditions can lead to increased metabolism and a higher oxygen demand. Waste accumulation can result in increased ammonia levels, again reducing oxygen levels in the confines of the pond.

By feeding your fish you may speed up the process, resulting in your fish becoming distressed more quickly. Try to avoid feeding during these periods or feed when it is coolest in the evening.

It's important to keep an eye on the oxygen and temperature levels in your pond over these hot periods and make any necessary changes to limit losses. Try to keep your pond topped up and always remember to dechlorinate or dechloraminate any water you add to the pond to ensure that it is rendered safe for your fish.