Scores of fish have washed up dead in water near a Nottinghamshire village, after oxygen levels depleted.
The Lily Ponds, near Radcliffe-on-Trent, are home to large numbers of tench, bream, carp and small pike.
But after the country’s heatwave in the previous week, the fish were starved of the air in the water they needed to breathe. It is understood that the oxygen levels depleted after blooms of blue-green algae – officially called cyanobacteria – appeared in the water.
“It was horrible,” said Councillor Anne McLeod from Radcliffe-on-Trent Parish Council. “Apparently it’s happening all over the place because of the hot weather, so there’s less oxygen dissolved in the water, and they’re suffocating. It’s as simple as that.”
The fish appear to have died between Saturday afternoon and Sunday morning, according to local reports. Cllr McLeod visited after being alerted to the issue at around 10.30am on Sunday, and described the sight.
“The water looked like pea soup, so there must be some algae present,” she said. “Unfortunately we can’t remove the fish, so nature will have to take its course and we’ll have to wait for foxes and herons to eat the fish. But it is quite a shocking sight.”
The Enviroment Agency explains that blue-green algae, of which a variety of species exist, are widely found in freshwater. It is not normally a problem.
But when growth conditions are perfect – for example, there’s adequate light, water flow and a good temperature fo the bacteria to thrive – numbers can increase. These increased periods of growth are called blooms, and can have a negative effect on the appearance, quality and use of the water.
They can smell and block the surface of the water, causing it to appear green. This can prevent sunlight getting to plants in the water.
The algae photosynthesise during the day – adding oxygen to the water – but consume it at night. This means oxygen levels can be very low in the early morning and can suffocate fish and other creatures – especially when there is a lot of the bacteria about.
A sign has been put up at the site advising children and dogs to stay away. Blue-green algae can produce toxins, although not all do.
It is best to stay away, however, as they can kill animals and cause rashes if they come into contact with human skin or illness if swallowed. It is not possible to tell which algae is toxic and which is not just by looking at it, so it is best to assume they are.
Mark Baker is chairman of the Radcliffe-on-Trent Angling Society, which rents the pond for fishing. The group has examined the water and says that not all the fish are dead – mainly just the smaller ones.
“Some fish are more hardy than others,” said Mark. “And there’s not a massive head of stock down there anyway – it’s a very natural pond. But there’s not a lot we can do.”
In some rivers, canals or ponds, oxygen levels could be restored through the use of aerators and other methods of artificially introducing oxygen back into the water. However, this requires a generator or electricity, and there is no power supply near the Lily Ponds, which are in a completely rural area.
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