But the bacteria normally present in the water must have oxygen to do their part in breaking down the waste. Water acquires this all important oxygen from the plants that grow in the water itself. These plants use sunlight to turn carbon dioxide present in water into oxygen. The life and death of any body of water depends mainly upon its ability to maintain a certain amount of dissolved oxygen. Without it they suffocate.
Trouble begins when the wastewater load is excessive.
Waste in the water will decay and the water will begin to give off odours. If carried to the extreme the water could lose all of its oxygen resulting in death of both fish and the beneficial plant life. Since dissolved oxygen is the key element in the life of water, the demands on it are used as a measure to tell how well a treatment plant is working. At the Wastewater Treatment Plant There are different stages of treating wastewater - primary, secondary and advanced. North Shore City's plant uses all these stages and plans to install additional tertiary treatment later if required.