The photo was snapped back in July when as Clary completed the 200m Backstroke Final in Shanghai.
According to Fuck Yeah Fluid Dynamics:
Surface tension arises from intermolecular forces between water molecules. In the bulk of the liquid, any given water molecule is being pulled on in every direction by the surrounding molecules, which results in zero net force. At the surface, however, molecules only experience forces from those to the side and below them. As a result, these molecules are pulled inwards, forcing the liquid to take on a form with minimal area.