The underwater marker consists of a threaded spherical body covered in a retro-reflective tape that is designed to work well underwater. Ordinary passive markers cannot be used since the retro-reflective properties are lost when the markers are underwater. These markers work both above and under water. These markers are available in five different sizes: 12 mm, 19 mm, 30 mm, 40 mm and 50 mm. When up close, the taped underwater markers can sometimes break up and be interpreted as multiple markers. For these situations as well as for long time use underwater, we recommend our Super-spherical underwater markers.