A stream with dissolved oxygen levels below 6 mg/L is likely to:

A stream with dissolved oxygen levels below 6 mg/L is likely to indicate a pollution concern because adequate levels of dissolved oxygen are crucial for the survival of aquatic life. Fish and other organisms rely on dissolved oxygen for respiration; levels below 6 mg/L can create a stressful environment for many species, leading to reduced populations or even fish kills if the levels drop significantly lower.

Low dissolved oxygen levels often suggest that organic pollutants are entering the water, triggering processes such as decomposition, which consumes oxygen and diminishes its availability for aquatic organisms. The presence of nutrient pollutants can also lead to algal blooms, followed by die-off and subsequent decay, further depleting oxygen in the water. These conditions can disrupt the equilibrium of the ecosystem, creating an unhealthy environment for aquatic life.

In contrast, supporting a wide range of aquatic life, being ideal for fishing, or having minimal ecological impact would be characteristics of a healthy stream with ample dissolved oxygen and minimal pollution.