Lifeguards need to expect to see foam.  It is present in almost all drowning victims and there is a lot of it!  Are they prepared?  Do they know to blow through the foam?

 From Drownings Present as Hypoxic Event in the Journal of Emergency Medical Services:

"One complicating factor in the treatment of a drowning patient is the presence of copious amounts of foam in the upper airway. It was previously thought that this fluid was coming from the lungs, but it’s now recognized that much of it comes from the stomach. Ancient and outdated drowning treatments were directed at “draining” the water from the lungs either through the Heimlich maneuver or inverting the patient. All attempts to suction or clear this foam from the airway only delay much-needed oxygenation and go against most dogma of airway management—the patient is dying from cerebral anoxia and not foam in the upper airways. Thus, prehospital providers should focus on oxygenating and ventilating the patient and not on aggressive suctioning. Of course, if cardiac arrest is present, CPR should be initiated and necessary ALS measures provided."