If water in a stream is at 20 degrees C with nine mg of oxygen per liter, what could it indicate?

The condition of the stream water at 20 degrees Celsius with nine milligrams of oxygen per liter suggests that it lies within an acceptable range for aquatic life, particularly for species such as rainbow trout. Rainbow trout thrive in waters that are cooler and well-oxygenated. Temperatures around 20 degrees Celsius, while on the higher end of their preferred range, can still support their survival, especially if oxygen levels are adequate. Nine milligrams per liter is typically sufficient for many freshwater fish, including trout, which generally require about 6-8 mg/L of dissolved oxygen for survival.

The presence of enough dissolved oxygen indicates that the stream is likely functioning well ecologically, ruling out significant pollution or anoxia, which would typically be indicated by lower oxygen levels. Thus, the specified conditions imply a favorable environment for rainbow trout, supporting the assertion that the stream is comfortable for them.