Pond Boss Forums INTRO Questions & Observations ice holes

bubbles in the ice can be caused by many things.....beavers/muskrats exhaling under water is one. Fish relieving their air/swim bladders is another. Turtles are another source of bubbles. Decomposition of bottom material can cause methane and other gasses which cause bubbles. Anything that disturbs the bottom of the pond can release trapped gasses in the muck - fish, turtles, etc.

Your holes with jagged edges, clear in the middle and spread throughout the pond....are likely drain holes which are sometimes called octopuses
http://lakeice.squarespace.com/drain-holes/

You can see a couple drain holes on my pond here


Here are some springs - this is an old sand pit that is completely fed by ground water infiltration with a south to north flow. This picture is looking west. This was early ice, after a warm rain - you can see all of the small drain holes in the foreground


High flow springs or warm water springs will not freeze easily, and are typically very hard to spot depending on the surrounding ice.

I would say you have a small spring or a critter keeping that hole open

Keep in mind that water is most dense at 39 degrees so even a small flow could help circulate enough warmer water to the surface to create a spring crater