When an aeration system is initially installed there will be a period where the aerator will draw up large amounts of poor-quality water and some organic debris from the bottom that can have an impact on the water quality.
It will increase the oxygen demand and potentially raise the phosphorus and nitrogen levels for a short period of time. This is a critical time for the lake, but as long as the aeration system is running it will be able to combat these issues and in time the lake will turn around.