I've been pondering this since the presser yesterday. I've returned to my initial view. NB entered the water. The speed of the police reaction and the immediate, seemingly vehement belief that despite this being a lone female disappearance, this is a MP enquiry and that NB went into the water, is down to one of two areas of knowledge not in the public domain: family information about NB or someone reporting a glimpse/sound of something/someone in the water that cannot been verified, but was persuasive to LE. No idea why this wouldn't be in the public domain, btw.
PF is doing a great job, and I'm glad he's doing it, but I've felt myself getting sucked into the PR line of 'if PF can't find her, she's not there' reasoning. I've had a word with myself about that, and I'm back with the sad, sad reality that a body in the water might not be found.
All MOO.