Chertsey lake tested after Zane Gbangbola flood death
Tests are to be carried out on a lake next to the home of seven-year-old Zane Gbangbola who died during last winter's floods in Surrey.
Post-mortem tests were inconclusive and a pathologist's report said the cause was carbon monoxide poisoning.
But his parents believe he was killed by hydrogen cyanide fumes released from floodwater from the lake, which was built over a former landfill site.
Defra confirmed that environment secretary Liz Truss ordered the tests.
Mrs Truss wrote to the Environment Agency after meeting Zane's parents Kye Gbangbola, 48, and Nicole Lawler, 37.
Mr Gbangbola, who was paralysed by the incident that killed his son, welcomed the move but said: "The government needs to ensure something like this never happens again."
'Urgent inquiry needed'
He said they had lost a son but he claimed thousands of other people could be at risk.
"There needs to be an urgent inquiry, not just into why Zane died, but into historical landfill sites in the UK and the consequences of them being flooded," he said.
It is understood tests for the presence of any toxins in the lake will be carried out imminently.
Both Defra and the Environment Agency said their sympathies were with Zane's family and added the incident had been investigated by Surrey Police and other agencies.
In December, Surrey Police said a petrol-driven pump had been seized from the family's home in Thameside but detectives found there was no criminal case to answer on the part of the hire company that provided the equipment.
An inquest is still to be held.