Divers Play Hockey Upside Down In Frozen Lake, How Did The Puck Stick To The Ice? [MYSTERY VIDEO]

Divers from Siberia staged what must count as one of the most innovative hockey tournaments ever when they took their pucks and sticks into a lake to play upside down on the ice, near Temirtau village, Kemerovo region.

Take a look at this video and let us know how you think they did it.  Keep in mind, the lake is frozen.  They break through the ice and play UPSIDE DOWN under the frozen lake top.

At the end of the video they show the puck.  Is it Styrofoam?  Styrofoam would float but would be too light to hit around as in the video.  Is there something in the Styrofoam to make it heavier?  How'd they do that?