There are specialist water recovery search dogs that sit on boats or work along the water’s edge and indicate when they detect human/cadaver related scents from released gases (as seen in photos from this search).
I would imagine some cadaver dogs would also do this from the water’s edge - but am not sure if they are trained for it specifically. My guess would be that given that most search/detection dogs are trained to only indicate ‘at source’ my guess would be that a handler would note a point of interest as a dog tried to locate the scent - but that they wouldn’t indicate a clear find. (Hence the need for dogs trained in water recovery)
I’m not sure how many specialist water search dogs there are in the UK, or indeed cadaver dogs - my understanding is that both can be very challenging to train and qualify for as a civilian/volunteer, given the availability of scent for training and the levels of training, confidence and certification needed for a dog whose ‘evidence’ may be needed in court.
More info on drowned victim search dogs at
Home - The National Search And Rescue Dog Association