Water quality refers to the chemical, physical, and biological characteristics of water, including temperature, salinity, turbidity, dissolved oxygen content, and concentration of contaminants. Water quality is crucial to support the many animal and plant organisms that live in it. Marine and freshwater environments can be very sensitive to changes in water quality, especially dissolved oxygen concentration, salinity, nutrient levels, and presence of contaminants or chemicals. As offshore wind and marine renewable energy devices are placed in the water, changes in flow may occur around this new obstruction due to energy removal and may affect the distribution of these water components. While the effects of individual devices may be localized, arrays may have a greater impact on changes in water quality in the farfield environment and on ecosystem processes. Estuaries may be the most susceptible to impacts, as researchers theorize that significant energy extraction may increase vertical mixing while decreasing flushing. This may result in positive impacts such as higher concentrations of bottom water dissolved oxygen, while also negatively affecting water quality by increasing contaminants and phytoplankton production. Numerical models are often used to estimate changes in water quality, but it is difficult to quantify change in such a complex system with natural variability and climate change.