The body of a four-year-old boy who slipped from a jetty is believed to have been washed out to sea after specialist sonar equipment failed to find him, experts said on Wednesday.
Dylan Cecil was on holiday with his family when he stumbled into the muddy water at Burnham-on-Sea, Somerset, at 6pm on Sunday.
His mother, Rachel McCollum, said he fell into a "whirlpool" and she knew immediately that she would not see him again despite her desperate efforts to save him.
Volunteers from the UK underwater rescue organisation SARbot used specialist sonar equipment to scour the water for Dylan's body today.
But after spending hours on the water his body could not be found.
The organisation was using sonar equipment which is more sensitive than that used by police and had earlier said that if the youngster's body was still in the area, they would find it.
This evening, Duncan Winsbury, chief executive of SARbot, confirmed the search had been brought to an end.
"We've just completed the search and have searched the whole bay and we've not found anything," he said.
"We believe that the currents may have taken him right out to sea now, he's certainly not in the bay."
Dylan, from Kettering, Northamptonshire, was visiting his grandparents with his mother, father Darren Cecil and two younger sisters, aged one and three.
He had wanted to get a closer look at the sea when he slipped off the side of the jetty and disappeared beneath the water.
His parents desperately tried to rescue him, but were unable to reach their son and had to be pulled from the water by passers-by.
The Coastguard and police launched a large search and rescue operation after a member of the public saw Dylan's parents attempting to rescue him.
The search for Dylan, who was wearing a T-shirt and shorts, was called off at 4.30pm on Monday but volunteers have continued to look for him in order to bring closure to his family.
The SARbot UK team, based in Weymouth, Dorset, were using side-scan sonars that were designed to detect human remains underwater.
Four volunteers from the charity started their search this morning, scanning an area off the beach, and later concentrated on a five-mile channel where they believed Dylan's body may have been located.
Mr Winsbury said: "The police, the Coastguard and the RNLI think that we have searched much more than they could have expected to have been searched and more thoroughly.
"Because nothing has been found on this search, they have decided to wind the search down based on that.
"We do offer our deepest sympathies to the family. That is the whole reason we exist as a charity, to assist people like this; in fact, some of the team members have lost family members in the same way.
"We don't give people false hope, but we like to give people hope where we can.
"Unfortunately in this case, it's the old saying 'We can't find what is not there'."
Dylan's family remained at the scene today and were being updated about the recovery operation.
Ms McCollum told the BBC yesterday: "He (Dylan) was literally not even a metre away from me and he was jumping and slipped and I watched him fall in.
"I jumped in straight after him - what more could I do? He went. I knew as soon as I jumped in I was not getting him back."
She thanked everyone who had searched for his body and implored people not to give up looking for her "gorgeous" and "bubbly" little boy.
"I just want my son back," she added.
The water off Burnham-on-Sea has one of the highest tidal rise and fall ranges in the world and the shoreline is notorious for its dangerous mudflats.
The local authority, Sedgemoor District Council, said it was satisfied that all its procedures were followed correctly and there are many warning signs along the beach, esplanade and on the jetty hut.
But it said it is also carrying out an internal review "to establish all relevant information".