Why should high temperature water not be dumped into a river or lake?

High temperature water is detrimental when dumped into natural bodies of water primarily because it increases the oxygen demand and can cause deaeration. When hot water is released into a river or lake, it raises the temperature of the receiving water body. Warmer water holds less dissolved oxygen, which is crucial for the survival of aquatic life. A spike in temperature can lead to an increase in metabolism and respiration rates of aquatic organisms, which further drives up their oxygen demand. Consequently, with lower levels of dissolved oxygen in the water, fish and other aquatic organisms could experience stress or even die due to lack of oxygen, leading to a decline in biodiversity and disrupting the ecosystem.

The other options, while they may contain some merits in specific contexts, do not address the primary environmental concern associated with the dumping of high temperature water. For instance, while dumping high-temperature water could potentially affect pH levels or plant growth, the most critical and immediate impact is related to oxygen levels and the health of aquatic life. The attraction of harmful bacteria is also a concern, but it is not the most pressing issue compared to the impact on dissolved oxygen. Thus, the increase in oxygen demand and consequent deaeration is the reason why high temperature water disposal into lakes or rivers is problematic.