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There is a video where a couple of people are walking on extremely clear lake ice.

Usually, lake ice is far less clear, what conditions on this lake would lead to the unusual clarity?

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  • I think this often with puddles too, some completely clear and others very white ice!
    – Aravona
    Commented Mar 18, 2019 at 11:09

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Conditions that can lead to clear ice such as this are:

  • Water with few impurities causing less scattering of light: This lake does not have any water flowing into it, therefore rain is the only source of water
  • Freeze the water slowly so that impurities and air bubbles can rise to the surface, and in the case of air, escape.
  • The area of the lake in the video is shallow, therefore light has less distance to travel and be scattered before it is seen.

Source: Physics Buzz

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    +1 and to add the lack of follow-up rain and snow to scuff and cover parts (i.e. one slow continuous hard freeze).
    – Mikey
    Commented Mar 18, 2019 at 15:15
  • also: no wind (no ripples). I'm not so sure about no inflow, though I'd agree on low flow. No inflow but outflow will lead either to bubbles or cracks as the water level goes down.
    – cbeleites
    Commented Mar 21, 2019 at 0:05
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The primary occluding agent is air bubbles that separate from the water as ice forms.

You can get clear ice cubes for drinks by heating the water first to expel most of the air before you freeze it.

Water that freezes slowly allows more time for air to move out of the way. A small current that move air bubbles along will allow small bubbles to be herded along and the area that is left behind will 'catch up'

I have seen clear ice on the Red River north of Winnipeg. The Red is normally a silty river, but the much slower current in winter, with no wind disturbance once an initial layer of ice formed allowed the silt to settle.

Through the thick ice we could see occasional large (several inches across) bubbles where 'riverbed farts' got trapped under the ice. Twice I saw large carp swimming several feet down.

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