English mother-of-two Nicola Bulley drowned after entering cold river water and there is no evidence anyone else was involved in her death, an inquest has been told.
Two witnesses said they heard a scream coming from the area of the River Wyre in Lancashire where the 45-year-old was last seen on the day she disappeared.
Drowning experts told the inquest into her death at Preston Coroner's Court that entering cold water can cause a victim to gasp and inhale water and drown within seconds.
Professor Michael Tipton, a world expert in drowning, said there would have been a "fairly rapid incapacitation" after Ms Bulley went into the river on the morning of 27 January, which could have been as cold as 3C.
It may have been just seconds before she began to lose consciousness, the hearing was told.
Prof Tipton said he agreed with UK Home Office pathologist Alison Armour, who conducted a post-mortem examination and concluded Ms Bulley drowned.
He said Ms Armour’s finding of water in the stomach and lungs is consistent with a "gasp response" under water, with liquid entering the body’s organs.
Ms Bulley vanished after dropping off her daughters, six and nine, at school, and taking her usual dog walk along the river in St Michael’s, Lancashire, on 27 January.
Her mobile phone, still connected to a work Teams call, was found on a bench overlooking the water.
Her body was found in the river around 1.6km from the bench, on 19 February.
Prof Tipton told the inquest: "In my opinion, given the nature of the likely entry into the water, I would suspect Nikki had a gasp response under the water, initiating the drowning process.
"On the balance of probability there was a fairly rapid incapacitation due to the cold shock."
It could have been an estimated "20 to 30 seconds" before Ms Bulley lost consciousness, the inquest heard.
Two breaths of water would have been a "lethal dose" for someone of Ms Bulley’s size, Prof Tipton said.
Cold water expert Dr Patrick Morgan said: "On the occasion that the individual has taken that initial gasp on the surface of the water and then gone below, the duration would be 10 seconds that you could hold your breath and very likely one or two seconds at best."
PC Matthew Thackray, a police underwater diver, said the area where Ms Bulley is believed to have gone into the water has a steep slope.
He added: "The river was 4C, so almost freezing, and if she fell in, the muscles would probably seize, making it difficult to swim properly."
One witness - nurse Helen O'Neill - said: "I heard a scream, it’s not an alarming noise, it was just over in a couple of seconds.
"There were no other sounds for me to be concerned about."
Another witness, Veronica Claesen, said: "I was just about to get into the car and I heard a scream. A very short scream and my immediate thought was, 'Somebody is having a bit of fun at the back of the graveyard’."
Police analysis of Ms Bulley's iPhone and Fitbit watch showed the phone’s last human generated interaction was at 9.18am and the watch stopped recording steps beyond 9.30am.
This suggested she entered the water between those two times, the hearing was told.
Her partner Paul Ansell will give evidence to the inquest tomorrow.
Ms Bulley, a mortgage adviser, was immediately deemed a "high risk" missing person when she disappeared, sparking a huge police search operation, with hundreds of search volunteers and intense media and public interest.
Police urged people not to speculate and maintained from early on there were no suspicious circumstances and she may have gone into the water due to an "issue" with her springer spaniel dog Willow.
Ms Bulley's family and friends said they did not believe the police "theory" and urged people to continue searching.
Mr Ansell, her partner of 12 years, gave TV interviews appealing for help - saying their daughters wanted their mother home.
As the days passed and speculation continued online, Lancashire Police revealed Ms Bulley had struggled with alcohol and perimenopause.
This prompted widespread criticism of the force, with Home Secretary Suella Braverman and Prime Minister Rishi Sunak questioning the police approach and an investigation being opened.
Shortly before the inquest began, coroner Mr Adeley addressed the social media controversy surrounding Ms Bulley's death.
He said the inquest would deal with only "proportionate evidence from reliable sources and not ... explore all the theories by those who contributed to social media".
"At the centre of this inquest are two children who have lost their mother, a partner and parents who have lost a daughter," he added.
Mr Adeley said anyone with the "slightest idea" of disrupting the hearing would be dealt with "immediately".
