Buckle for adjusting the strap in equipment for practicing water sports, such as diving goggles, swimming goggles or the like, said strap being provided at at-least one end with a plurality of transverse reliefs, said buckle comprising a body provided with means for driving said end of the strap and with an engaging tooth which is normally kept in a position engaged with said reliefs of said strap, against said drive means, there being envisaged operating means able to disengage said engaging tooth from said reliefs, comprising means with an inclined surface co-operating with said engaging tooth and movable in a direction substantially parallel to the longitudinal axis of the end of said belt.