Dissolved oxygen measures the amount of oxygen dissolved in water that is available for use by aquatic plants, shellfish, fish, and other animals.

Oxygen gets into the water by diffusion from the surrounding air and as a waste product of photosynthesis. Sufficient oxygen levels are required in order to provide for life forms. Where there is low dissolved oxygen concentrations, aquatic animals are more vulnerable to adverse effects of other stressors.

Lake trout are the most sensitive local species and require a minimum of 6pmm dissolved oxygen to thrive.

In lakes that go anoxic (lose all oxygen) at the end of the summer or winter, phosphorus can be released from the sediment and may result in a late summer algae bloom.