An underwater forensic expert says he does believe Nicola Bulley is in the River Wyre.
Specialist Group International (SGI) were drafted in by police looking for the missing mum-of-two today after founder Peter Faulding offered his services over social media.
The firm is used by police forces across the south-east, apart from London, and were willing to work for nothing as the search moved into its 11th day.
Mortgage broker Nicola, 45, vanished on January 27 while taking her springer spaniel Willow for a walk in St Michaels on Wyre.
Speaking at the scene, Mr Faulding said: "I do believe she's in here from the evidence we've got at the moment.
"Everything is pointing to the river.
"There doesn't seem to be a third party involved."
He told the Mirror last night SGI's 'top of the market' 18,000khz side scan sonar would likely find Nicola almost immediately if she was in the river.
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Mr Faulding said he believed if she drowned she would have likely got "snagged" within around 500 metres of the point of entry.
He said: “If Nicola is in there, we will find her. If she’s there, our sonar will pick her up straight away.
“I will see a body on the bottom. We are dealing with about 10 drownings every summer. We always locate within the hour. It’s that quick, it’s that good.
“Nicola wouldn’t have gone far if she was in this river because it’s got shallows and she would get lodged. There’s no way she would have gone out to the estuary.
"The river’s not in flood, it’s benign.”
However, at that stage he said the situation appeared "odd" and he wasn't necessarily confident she was in the river.
It's unclear what has changed his mind.
Explaining how the equipment works, he said: "The sonar will highlight every stick and stone on the bottom.
"It’s as good as that.
"As I tow it along I get a picture on the screen in front of me.
"The sound wave gets sent across the river bed and then that data gets picked up and comes back and is analysed by the computer, and I can actually measure how long a target is. We can then put a diver in to confirm that target."
He said if Nicola had drowned and her body had been taken downstream, the team and sonar can cover around 10 miles a day.
