Water search K-9's are trained to "alert" on the scent of a human underwater which rises to the surface and is then carried on the wind.  These dogs may be worked from a boat or from the shoreline, when the wind is favorable.  Water search dogs may have their basic training in live-find wilderness search, cadaver search or both.   They may also be used to search for victims underneath the ice if the handler has the training and equipment to do so safely.  The biggest advantage to using water search K-9's is to limit the size of the area that must be searched with other resources, especially divers.