The physico-chemical characteristics of water can indeed be affected by all the factors listed, but the most pronounced and prominent change tends to originate from effluents, making option 3 the correct answer.

Option 1, aquatic macrophytes, can influence the water quality, as they take up nutrients and can alter the oxygenation and acidity levels of water. However, this is usually in a balanced, sustainable way as part of a natural ecosystem.

Option 2, aquatic fungi, can similarly lead to changes, as they play a role in decomposition processes, but their effect on the whole water body again is usually not as drastic unless the ecosystem is disrupted.

Option 4, evapotranspiration, can cause concentration of salts and other substances in the water, affecting its physico-chemical properties. But this process usually takes a significant amount of time.

However, effluents, option 3, often include industrial or domestic waste and can drastically upset the balance of a water source, adding a wide range of chemicals and leading to major and swift changes in the water’s physico-chemical properties. That`s why option 3 is generally the most impactful.