What is the enviroment in which water will come out of an ice fishing hole? I have watched some videos on YouTube of people cutting holes in ice and water not just finding equilibrium in the hole, but water actually coming out of the hole along with many fish. There has to be more pressure under the ice in order for water to come out of the ice fishing hole in any substance quantities. Even if a lake is covered in ice and snow, the density should be less than that of the water and weigh less than that of the water displaced, ensuring buoyancy.  What conditions must be present in order for this to occur? In addition, to add a little biology to the question, how and or why are there so many fish that come through the ice hole?  The density of fish in the body of water can not be as dense as the amount of fish per gallon that come through the hole. I have included a link to a YouTube videos to visually demonstrate my question.   
https://www.youtube.com/watch?v=MHf7IoNGVfo 
 A: The ice surface is sloping. This is clear on watching the video in which water issuing from the hole is preferentially flowing to one side only. Water gushing out of the hole is then simply explained by hydrostatic pressure difference due to a difference in height between different points on the water body and has nothing to do with density differences. The current caused by upwelling water must have been strong enough to pull fish from underneath the ice surface, at least those unfortunate ones close to the surface. As to why there are so many fish at that spot is not really a fluid-dynamics question. People must have dug a hole where by previous experience they knew that they are going to find a lot of fish.
P.S. This is the second question on fishing-by-unconventional-means I have encountered in a week. Must be coincidence!
A: I have not watched the video but I did grow up in northern Minnesota, so ice fishing was a common activity.  Yes, ice1 is generally less dense than water, but it is temperature-dependent.

Even if a lake is covered in ice and snow, the density should be less than that of the water and weigh less than that of the water displaced, ensuring buoyancy. What conditions must be present in order for this to occur?

Even though the ice is buoyant, that does not mean water will not come up initially after puncturing the ice for two reasons:


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*dragging the auger out pulls water with it; and

*you are locally depressing the ice by standing on it or having some large object nearby (e.g., a vehicle).


In general, the thinner the ice the more of an effect the 2nd will have on water coming up through a fishing hole.  I was out once when we were sitting in about an inch of water because the ice was thin enough that our own weight mattered (though still thick enough not to be dangerous, surprisingly).

In addition, to add a little biology to the question, how and or why are there so many fish that come through the ice hole?

Again, I did not watch the video, but I am guessing the effect is similar to that of a siphon if lots of water is coming out of the fishing hole.  That is, the fish were dragged along by the flowing water similar to if they were in a river and drifting with the current.
Footnotes


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*Note that the majority of ice most people encounter on Earth is called $Ice \ I_{h}$.

