Police searching for missing Nicola Bulley say something "could have happened" with her dog that caused her to approach the nearby river and potentially fall in.
The 45-year-old mum had dropped her kids off at school last Friday morning before taking springer spaniel Willow for a walk along a towpath in St Michaels on Wyre.
Her phone was found on a bench and the dog was running around nearby without its harness or lead.
The device was still logged into a work group conference call, although with her camera and microphone muted, and the meeting had finished.
Superintendent Sally Riley revealed today that the investigators' main hypothesis is that she accidentally fell into the river.
She told reporters in a press conference that officers are "as sure as we can be" that Nicola did not leave the area.
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Supt Riley said: "At the point where the bench is located there is quite a steep drop to the river, albeit not high, it is steep.
"And therefore whilst I don’t want to speculate as to what may have happened, it is our working hypothesis that she has entered the water accidentally and that’s why there is no physical evidence on the field."
She confirmed the mum can swim, and said due to the different water depths searchers have been both wading in the River Wyre and diving underwater.
The superintendent said after a "thorough" search of the immediate stretch of water, investigators have not found any conclusive evidence.
She went on to say: "The dog was off the lead, this was normal for the dog to run about and Nicola was on a teams call, which again it would be normal for her not to participate in actively and just have the phone to listen in, effectively.
"Anything could have happened with the dog whereby Nicola may have gone - and I don’t wish to speculate, we don’t know - but it is possible the dog was loose and off the lead that there may have been an issue with the dog that led her to go near to the water’s edge.
"She puts the phone down momentarily and Nicola may have fallen in. That is a possibility," said Supt Riley.
She confirmed the dog was dry when found by other walkers.
"We don’t believe the dog was in the river because the dog, we believe, was dry and the witnesses have not described the dog swimming or jumping into the river.
"We don’t know why Nicola may have entered the water if she did," she added.
