What is a major concern regarding water pollution from the dairy industry?

A significant concern regarding water pollution from the dairy industry is the high levels of biochemical oxygen demand (BOD) and suspended solids it generates. Dairy operations typically produce large amounts of organic waste, which includes manure and wastewater from cleaning dairy facilities and processing milk. This waste is rich in nutrients and organic materials, leading to elevated BOD levels when it enters water bodies.

High BOD indicates that there is a substantial amount of biodegradable material in the water, which microorganisms can break down. While this breakdown is a natural process, if the levels are too high, it can consume oxygen in the water, thereby harming aquatic life. Additionally, the suspended solids can lead to sedimentation issues, affecting water quality and clarity, and can further disrupt ecosystems.

The other options, although they might seem relevant, do not represent the primary concern associated with the dairy industry's impact on water pollution in the same way that high BOD and suspended solids do. For instance, while heavy metals and oily waste can be troubling in certain scenarios, the predominant issues from dairy operations predominantly lie in the organic waste produced, which leads to the problems highlighted in option C.