The lake you see in the video and photos is a shallow lake made up of water that has melted on the surface and pooled on top of the ice below it.
Arctic sea ice has be decreasing every year. Last summer’s minimum arctic ice cover was the least ever recorded. This year’s maximum winter arctic ice cover was the 6th lowest recored since the 1970s.
This small lake at the north pole is a bad thing as the darker lake absorb more sunlight which in turn melts more ice and creates larger lake and contributes to the break up of arctic sea ice.