They do not discriminate scent e.g. they do not look for specific people but will look for anyone that is in the water.
Once the dog finds a missing person they will ‘indicate‘ with a bark or by pawing at the water.
On finding the scent of the missing person the handler ‘rewards‘ the dog with their favourite toy and/or food whilst heaping lots of praise on them.
It is this ‘game’ through years of training that drives the dog to find the missing person.