The rancid smell of rotten fish met New York City residents as they strolled along the Hudson River in December 2020. Walkers and environmental action groups reported hundreds of dead fish washing up on the river’s banks from Sleepy Hollow to Yonkers, or sightings of the sea life visibly suffocating in the city’s harbour.
While there were multiple causes of the die-off, one significant factor is hypoxia – which is when the amount of oxygen dissolved in a body of water drops below a certain threshold. Without enough oxygen in the water, fish and many other forms of sea life may die en masse, leaving the surrounding area lifeless.
Hypoxia (or anoxia, where there is no oxygen present in water at all) can happen naturally. There are certain areas of the ocean that contain low levels of oxygen due to their location and limited inflows of new water. However, this phenomenon is greatly exacerbated by human activity; the number of coastal dead zones has increased...