Pond Boss Forums INTRO Questions & Observations Bluegill Die off

Could very well have been an O2 crash. All it takes is 2" snow and 2" cloudy ice to stop the majority if not all sunlight from getting to the water. Phytoplankton produces a lot of O2 during the winter when the plants aren't growing, but if there is no sunlight they utilize O2.

That's why having a large amount of water in the pond in regards to the biochemical demand and also having 10% of the surface area open to the air is the ticket for minimizing winterkill when ponds are iced over and then snowed upon. I've seen a winterkill in less than 2 weeks in a pond without winter aeration and not a lot of water (5' depth max).