Experts warn more heatwave fish deaths may occur
Owen Sennitt/BBCExperts believe mass fish deaths could become increasingly frequent due to climate change after thousands perished in a river heatwave "disaster".
Norfolk Wildlife Trust gave the warning following an incident on the River Wensum in Norwich last Thursday.
The Environment Agency believed it was caused by heavy rainfall flushing in contaminants from surface water drainage systems at a time when the river was already suffering from depleted oxygen levels caused by prolonged dry, hot weather.
Helen Hebditch, director of nature recovery at the Norfolk Wildlife Trust, called the conditions a "recipe for disaster".
Owen Sennitt/BBCHebditch added: "In a summer characterised by shocking wildfires, this is yet another example of how our changing climate is having a devastating impact on our wildlife.
"Drought conditions are depleting already low water levels, and sustained high temperatures lower water oxygen levels, leaving river wildlife such as fish struggling to breathe.
"This means our rivers, and the wildlife that calls them home, are extremely vulnerable. Add to this heavy rain washing pollutants into the water from nearby roads or sewage discharge, and it's a recipe for disaster."
Owen Sennitt/BBCHebditch said the incident was "particularly significant" due to the River Wensum being a protected chalk river. She added that these events were likely to increase in frequency due to climate change.
There have also been reports of fish found dead elsewhere in the county on the River Yare in Trowse and at Cantley, east of Norwich.
Anglian Water said a storm overflow discharged at the Trowse pumping station on the River Yare for two hours last Thursday and subsequently people reported fish and other aquatic life in distress.
The company said it was working with the Environment Agency to investigate the incident.
Oxygen levels have now "improved significantly", the firm added.
Storm overflows are used to prevent flooding and discharge excess sewage and rainwater into rivers and coastal waters.
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The stretch of the River Wensum where the incident was discovered is a popular spot for paddle boarders and people using canoes, with multiple hire firms located in the city.
Anglian Water workers continue to clean up the Wensum, and Norwich City Council and the Broads Authority are also assisting.
Council workers said they had collected about 1,200 fish in two days, focusing on larger species, while Anglian Water said it has collected 2,126.
People have complained there has been a strong smell along the river in the past few days.
Chris Goreham/BBCAnglian Water, which is continuing to monitor the river, said ammonia levels have returned to background levels and dissolved oxygen levels are improving.
The River Wensum stretches about 44 miles (71km) through Norfolk and is designated as a Site of Special Scientific Interest and Special Area of Conservation.
It is believed to be home to more than 100 plant species and rich invertebrate fauna, and is recognised as one of the most important chalk river habitats in England.
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