Can rapids act like lungs? 

All life needs oxygen to survive.  

This is true for fish eggs and fry.  

The oxygen levels are higher in running water  

than in calm water.  

 

The constant motion of the swirling water  

creates pressure differences between air and water.  

Oxygen is thus dissolved more easily in swirling water.  

Waves and whirls also mean that a larger amount of the water surface  

comes into contact with the air.  

 

The oxygen-rich environment means that many fish species  

seek out running water to spawn or breed.