Topic explanation

Standard explanation

Dissolved oxygen (DO) is molecular oxygen (O₂) dissolved in water and available for aquatic organisms and chemical processes.

Key points

• Beginner: Fish need oxygen too, but they obtain oxygen dissolved in water. If pollution causes microorganisms
• Intermediate: DO reflects the balance between oxygen entering or being produced in water and oxygen being consumed
• Dissolved oxygen is O₂ dissolved in water; aquatic organisms need it for respiration.
• Organic pollution can increase microbial decomposition and oxygen consumption, causing DO to fall.
• Use several measurements; appearance alone is not enough.

Labelled diagram