Normal magnifying glasses do not work underwater. The refraction index of glass is almost equal to water.
Our magnifying glass however does work and was especially designed to be used as a underwater magnifying glass. This diving glass is avaible since 2000 in several versions. By using an aspherical lens with a diameter of 11 centimeters the image distortion is minimal.
Nowadays this orginal magnifying glass is used by many divers and marine biologists. But it is also used in the off-shore industry and varying explorations.