Cold water can hold more oxygen than warm water leading to the higher readings compared to the summertime tests. The initial spike at the surface is probably due to the disturbance of the ice auger used to drill the testing hole but it could also be due to surface algae giving off oxygen right under the ice. The ice appeared to be approximately 12-15 inches in thickness. Oxygen drops off significantly after 30 feet due to biological activity and the ice cover prevents the wind from mixing the lake to add more oxygen. Since we have not typically monitored the oxygen over the winter it’s unclear if this is unusual or not.