Water searched for missing woman Danuta Domagalska
Specialist search teams have been focusing on ponds and slurry pits in the hunt for a Polish farm worker.
Danuta Domagalska, 27, worked at New Moor Farm, near Walworth on the outskirts of Darlington, but has not been seen since 6 August.
Durham Police investigating her disappearance appealed for her brother Piotr Lawniczak, 31, to come forward.
A team of officers has been searching the farm.
Mother-of-one Mrs Domagalska lives in a cottage next to the farm with her husband Marcin Domagalski, who is working with police as a witness, and her brother.
Det Supt Adrian Green, of Durham Police said: "Her husband is working very closely with us. He is very concerned, upset and worried. He is behaving as anyone would.
"If Piotr is listening I would ask him to come forward both for his sake and the sake of his family.
"It would be very helpful to his family and us if we could find out what has happened to Danuta as quickly as possible."
A team of officers searched the farm, and water searching specialists from Northumbria Police examined ponds and slurry pits.
Det Supt Green said Mrs Domagalska was popular on the farm and was "hard working and very friendly".
He said: "... She could be alive, she could be fit and well elsewhere, and she could be with someone else.
"But we have to be conscious... that she might no longer be alive and that's why we are searching the farm in great detail and will be for some time."
Mrs Domagalska's five-year-old son is being cared for by her mother in Poland.
Mr Lawniczak is 6ft 2ins (1.88m), slim, with short, dark hair. When last seen he was wearing a navy blue jacket with a grey hooded top and grey jeans.