What factor primarily affects the amount of oxygen that water can hold?

The amount of oxygen that water can hold is primarily affected by water temperature. As temperatures rise, the solubility of gases in water decreases, meaning warmer water holds less dissolved oxygen compared to cooler water. This is an essential consideration in aquatic environments, as temperature fluctuations can have significant impacts on the health of fish and other aquatic organisms that rely on adequate oxygen levels.

While the presence of fish, pH levels, and salinity can influence oxygen dynamics in a body of water, they do not directly dictate its capacity for holding dissolved oxygen as temperature does. Temperature is a fundamental physical property that governs gas solubility in liquids, making it the primary factor in this context.