• Lynne Melvin

Aerating in Winter vs Summer

Updated: Nov 19

Why Would You Aerate in the Winter?


Typically, the main reason to aerate over the winter months is to overwinter fish. It is critical to maintaining Dissolved Oxygen (DO) levels in the lake or pond over the winter months for the fish to survive. Some species, such as Northern Pike, can survive on 1 to 3 mg/L dissolved oxygen, whereas Trout species require 4-6 mg/L for optimal health.


Stages of Water


There are 4 stages of water, and the higher the stage, the more oxygen the body of water will use. The higher the DO levels going into winter, the better, as the dissolved oxygen reserves can be rapidly depleted depending on the lake or pond’s stage, as explained below.


Organic load in the water body impacts the amount of aeration needed over the winter months. It is associated with the stage of the water. When a lake or pond has a high amount of organics, it will be using a significant amount of dissolved oxygen known as biological oxygen demand (BOD).


Stage 1

Lakes/ponds with excellent water clarity – highly transparent water, often naturally blue or aqua in colour, low suspended solids, and low algae levels present. A healthy population of aquatic species. Visually appealing.


Stage 2

Lakes/ponds are commonly clear but can be murky for short periods of time. Smaller bodies of water and pond will form beds of submerged aquatic plants. Low levels of muck and aquatic growth on the pond/lake floor. An emerging healthy population of aquatic species and good biodiversity.


Stage 3

Lakes/ponds have excessive nutrients, especially nitrogen, ammonia and phosphorous. Established beds of submerged aquatic plants along the shoreline and several yards into the water. Often cloudy, murky water through most of the year. Algae will form as early as June/July and will become progressively more prevalent throughout the summer. Fish kills may take place in summer and winter. Diminishing healthy aquatic species.


Stage 4

Lakes/ponds have an extremely high level of nutrients especially nitrogen, ammonia and phosphorous resulting in cloudy murky water with continuous algal blooms. Excessive aquatic growth is thick and nearly choking out the lake/pond. Fish kills are often during summer and winter.


Aeration & Open Water


The amount of open water is another consideration as this is where the oxygen exchange occurs. Fish need DO to be healthy and as the level of dissolved oxygen drops, so does their survival rate. Keeping a large open water area allows the toxic gasses to escape and dissolved oxygen to enter, keeping the lake well mixed or known as de-stratifying.


De-stratifying the water body or breaking the thermocline (see picture for reference) is also critical.

The mixing releases the build-up of toxic gasses from the bottom of the lake or pond and maintains DO throughout the water column. Fish will naturally migrate to the aerated area, where the fishing will typically be better.


Although aerating through the winter is beneficial to the body of water, please note that it is best not to aerate during the winter if it is unsafe to have open water.

If you choose to aerate during the winter, it is crucial to mark the area and put proper signage in place to warn of the hazards. Firing up aeration early in the spring can be beneficial not only for the aeration benefits but also to remove the ice quickly, which reduces the potential hazard.


Aeration during the summer months will improve water quality, which reduces algae and aquatic weeds and will increase dissolved oxygen. Again, if the water is in a higher stage, the water will require more dissolved oxygen to improve its health. Adding dissolved oxygen to the lake or pond using fine bubble subsurface aeration will prevent fish kills, improve water for livestock consumption, reduce odour, and decrease algae, muck and aquatic growth.