Lancashire Police explained the theory during a press conference in St Michael’s, a village on the Wyre.

The mother went on the walk after dropping her two daughters, aged six and nine, off at school in the morning. Lancashire Police have confirmed she was walking along a path by the river just before 9am.

“What she was wearing could also be a factor,” Riley told the MailOnline.

“I don’t wish to speculate but the facts are that she was wearing a quilted, ankle-length gilet, which is a big coat, and underneath that there was another coat and then under that coat more clothing.

“She was also wearing ankle-length wellingtons. One would assume they fill with water when someone enters a river so all of that clothing is heavy, particularly on someone who is of slight build and only 5 foot three.”

Ms Bulley posted photos of herself exercising on the patch of the river where she was last seen on the running tracker app Strava.

In some of the photos, her dog, Willow, can be seen playing with the tennis ball.

On Monday, Superintendent Riley said her force were “keeping an open mind” regarding the whereabouts of the missing mortgage advisor but today said they were working on the hypothesis that she may have fell in the river.

She has urged the public to look out for any items of clothing Ms Bulley was last seen wearing.

Her friends, including Emma White, have shared appeals through a series of the television interviews. Ms White told the BBC that Ms Bulley’s daughters are continually asking where she is.

Riley said there were no reports of any shouting, screaming or other signs of distress and said no footprints were found on the river bank.

Talking to Sky News yesterday, her sister Louise Cunningham said: “There has got to be somebody who knows something and all we are asking is, no matter how small or big, if there is anything you remember that doesn’t seem right, then please reach out to the police.

“Get in touch and get my sister back.”

Police have spoken to a few potential witnesses but have so far been unable to gather any additional information to aid their inquiry from these sources.

Yesterday, they spoke with a witness who they had identified from CCTV because of help from the public but the source told police they didn’t have anything useful for them.