The instant invention is a valve for the top end of diving snorkels having a conduit with an open end above the water surface, and an underwater end that terminates in a mouthpiece. The mouthpiece provides a flow path between the conduit and the interior of the diver's mouth. The conduit's above water opening is in-line with the conduit's longitudinal axis. The top valve consists of a soft diaphragm mounted on a compound linkage. The linkage is attached to the conduit adjacent the top opening. A float activates the valve linkage whenever the snorkel descends below the water surface. As the open end of snorkel moves underwater, the linkage moves the diaphragm against the top opening, thereby preventing water from entering. When the top of the snorkel is above the water surface, the linkage moves the diaphragm to the side of the conduit, out of the respiratory flow path.