ANS:C - 5

In order to protect aquatic creatures, the dissolved oxygen content in fresh water streams should ideally never be less than 5 ppm (parts per million). Dissolved oxygen is vital for the survival of aquatic organisms such as fish, insects, and other aquatic life. Insufficient levels of dissolved oxygen can lead to hypoxia, a condition where oxygen levels are too low to support aerobic life, resulting in stress, illness, or death of aquatic organisms. While different species have varying requirements for dissolved oxygen, a concentration of at least 5 ppm is generally considered the minimum level necessary to support a healthy aquatic ecosystem. However, certain sensitive species may require higher concentrations of dissolved oxygen to thrive. Therefore, maintaining dissolved oxygen levels above 5 ppm is important for the protection and conservation of aquatic life in freshwater streams.