Check out this amazing video from southern Maine's Sebago Lake this week where skaters filmed the pristine translucency of the ice.  It's so clear you can easily make out the rocks and lake bottom below.

There have been a few more videos released this week of this incredible sight at this Maine lake.

Seeing this video reminded my of another video that I'd seen earlier this year from National Geographic sharing a man skating over pristine ice in Sweden.  This video could actually explain how the Maine skaters were supported on Sebago Lake in what seems like thin ice.

And then, there's this video from 2014 of someone walking on a pristine lake in Slovakia.

A great article about how ice can be so clear can be read at io9.gizmodo.com where it is referenced that the reduced number of impurities in the water (e.g. bubbles, snow, etc.) and the speed of the freezing effects the creation of "black ice" like that of the Sebago Lake video.