What are oils and grease known to do in receiving water?

Oils and grease, when introduced into receiving water bodies, commonly float on the surface due to their lower density compared to water. This characteristic layer prevents the exchange of gases, including crucial oxygen, between the atmosphere and the water below. Oxygen is vital for the survival of aquatic organisms; when oils and grease cover the water's surface, they create a barrier that limits oxygen diffusion. This can lead to detrimental effects on aquatic life, resulting in hypoxic or anoxic conditions, where there is insufficient oxygen for fish and other organisms to thrive. Therefore, the assertion that oils and grease float and inhibit oxygen from entering the water accurately reflects their environmental impact.

In contrast, the other choices incorrectly suggest beneficial effects or characteristics of oils and grease that do not align with their ecological consequences. They do not enhance water clarity; instead, they typically contribute to murkiness. Additionally, they do not lower water temperature, as they actually can increase temperatures in certain scenarios due to solar heat absorption. Furthermore, oils and grease do not enhance aquatic life; rather, they can disrupt ecosystems and harm the organisms that depend on a healthy aquatic environment.