Hopes of finding toddler Ruben Scott alive have faded as police spend a fourth day focusing on a large lake on a remote Cape York cattle station, failing to find any trace of the boy.

Cape Patrol Inspector Mark Henderson sat down with the Scott family on Thursday night and told them too much time had passed for young Ruben to have survived on his own.

“Last night I had to sit with the family and advise them the survivability of their son and grandson has now passed,” Inspector Henderson said on Friday.

He said the massive search across 1700 square kilometres had been “a very hard task”.

“We’ve given it our best but paediatric experts now tell us that survivability has passed.”

“That won’t stop our efforts. We won’t stop, we will continue to try to find young Ruben and bring closure for the family.”

Ruben’s heart-broken grandfather, Noel Scott said he had one hope left after being told the toddler is presumed to have died alone.

“Hopefully we can find Ruben today,” Noel Scott said on Friday, holding back tears.

“We are preparing for the worst.”

Ruben was last seen by his mother Natasha Scott at 5.44pm on Tuesday before he wandered away from the homestead on Koolatah Station – a vast, rugged property and known crocodile habitat – on the western side of Cape York Peninsula.

Several police and SES search crews spent the intervening days combing bushland and nearby waterways, with environment department officers monitoring the numbers of crocodiles in the area.

The best they can do for his family now is find his body.

On Friday their efforts were focused on a large lake that lies behind the homestead.

“They are being assisted by (environment department) officers who are helping us gauge the level of crocodile infestation in that area,” Inspector Henderson said.

He offered thanks to the army of volunteers and emergency personnel who joined the search for Ruben.

“We’ve had some 450,000 square acres to search,” he said.

Earlier, Ruben’s mother Natasha Scott thanked everyone for their support via Facebook, saying that she had “every person that can help, helping to find him”.

“I understand all you guys are shocked and worried but please, try to hold back from messaging me,” she wrote.

“I’m trying to organise heaps of things to help find him and am trying to hold myself together.”

The ABC reported the family has lived at the 1700-square-kilometre property since January.

-with AAP