GRCA monitoring network - dissolved oxygen

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River Water Dissolved Oxygen Data

Dissolved Oxygen (DO or O₂) is the concentration of free (not chemically combined) molecular oxygen (a gas) dissolved in water, usually expressed in milligrams per liter, parts per million, or percent of saturation.

Dissolved oxygen in water is to the critters that live in the water like air is to humans. If there is too little dissolved oxygen organisms living in the water will suffocate and die. Levels above 5 milligrams per liter (mgO₂/L) are considered optimal and most fish cannot survive for prolonged periods at levels below 3 mgO₂/L. Levels below 1 mg O₂/L are often referred to as hypoxic and whenO₂ is totally absent anoxic (often called anaerobic which technically means without air).

The amount of dissolved oxygen in the river water can be affected by a range or factors and processes going on in the river. Aquatic plants can impose a significant influence on dissolved oxygen. Plants produce dissolved oxygen during the daytime and consume dissolved oxygen overnight.

Some areas of the Grand River watershed have an overabundance of aquatic plants in the stream. This can create changes in dissolve oxygen during a given day. Several of the water quality stations operated by the GRCA exhibit large daily fluctuations in dissolved oxygen as a result of aquatic plants growing in the river.