The EPA stream quality indicator for dissolved oxygen in stream water is:

The Environmental Protection Agency (EPA) identifies a dissolved oxygen concentration of 6 mg per liter as a critical benchmark for maintaining aquatic life in streams. This level is generally considered the minimum necessary to support a diverse community of fish and invertebrates, which rely on adequate oxygen levels for survival. Maintaining dissolved oxygen at or above this threshold is essential for the health of aquatic ecosystems, as lower levels can lead to stress and mortality among sensitive species. Therefore, a dissolved oxygen concentration of 6 mg per liter is a key indicator used to assess the quality of stream water and indicate whether it is suitable for supporting aquatic life.