The correct answer is option 4: Reduction in the dissolved oxygen level of the stream water.

When large quantities of domestic sewage are continuously discharged into a stream, it can lead to various environmental consequences. One of the primary consequences is a reduction in the dissolved oxygen level of the stream water. Sewage contains organic matter such as food waste, human waste, and other pollutants. As the organic matter decomposes, it consumes oxygen from the water.

The decrease in oxygen levels in the stream water can be detrimental to aquatic life. Aquatic organisms rely on dissolved oxygen for respiration. When the oxygen level decreases, it can lead to hypoxia or even anoxic conditions, where there is not enough oxygen available for the survival of aquatic organisms. This can result in the death of fish, invertebrates, and other organisms in the stream.

Options 1, 2, and 3 are not correct because the discharge of domestic sewage does not directly increase algal bloom, increase stream water temperature, or reduce the carbon dioxide level of the stream water. Algal bloom can be a consequence of excess nutrients in the water, such as nitrogen and phosphorus, which can be present in domestic sewage. However, it is not stated in the question that these nutrients are present in