Eutrophication – How Dead Zones Form and How To Fix It

Every spring and summer a massive green plume forms along the coast of three U.S states in the Gulf of Mexico, creating the third largest oxygen depleted zone in the world, killing wildlife such as fish, oysters, crab, and shrimp. 

The cost of this plume to the U.S seafood and tourism industry is an estimated 82 million dollars a year. The cause of this is eutrophication from human activity. 


In short, eutrophication is a process where pollutants enter a body of water, which leads to unwanted plant growth. This growth causes a chain reaction that eventually leaves the body of water with too little oxygen to support life, leading to massive dead zones where nothing can live.
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Eutrophication causes an algae bloom on a lake

Just like us, plants need nutrients to grow. Plants on land get their nutrients from air and soil whereas plants below water get their nutrients from beds and water. Normally, there are enough nutrients in the water that plants don’t grow too quickly but also have enough nutrients to keep them alive. 

If there’s a big enough increase in the amount of nutrients in the water, plants and other life such as algae can grow very quickly, causing the entire surface to become covered in algae, just like in the Gulf of Mexico. When the surface is blocked, the plants at the bottom are blocked from getting sunlight causing them to die. 

As the algae on top also start to die, they sink to the bottom with the dead plants. Then, bacteria at the bottom of the water begin to consume all this material, but to do so they need to consume oxygen from the water. As the bacteria eat more and more, they use up more and more of the oxygen in the water. 

Eventually there’s not enough oxygen left in the water to support life. Water with so little oxygen is called hypoxic and can lead to the type of dead zones we see in the Gulf of Mexico.

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Frog in water covered by algea. This water may only be able to support very little life.

Eutrophication does happen naturally however, certain unsustainable human activities are often the cause because they significantly increase the amount of nutrients in nearby bodies of water. When eutrophication is caused by humans it’s often referred to as cultural eutrophication.


Phosphorus and nitrogen are two of the three primary nutrients that are really important for plants. Human activities release a significant amount of these two nutrients into the environment in unnatural or uncontrolled ways, for example sewage that is dumped directly into the water without being treated adds both phosphorus and nitrogen. 

As another example, farmers will give their crops phosphorus and nitrogen through the use of fertilizer to make sure their farms produce as much crops as possible. Water can then easily sweep unused fertilizer into nearby bodies of water when it rains.

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It may not look like it, but water can contain many waste differants pollutants. These pollutants can act as fertilizer for plants.

E-waste and battery mining for electric cars can contribute to eutrophication as well. This is because they are both made with metals that act as nutrients to plants. Normally, the metals are locked up in rock, but as e-waste or in metal extraction, they are made more available in the environment. 


Fixing eutrophication is complicated because it’s so widespread and the main causes of eutrophication change depending on where you are and the actions you take each day. If you live near fresh water bodies you may want to be most careful with limiting pollution that contains phosphorus since it’s the nutrient and shortest supply.

In fresh water systems this means just a small amount of phosphorus can cause a big increase in plant growth. 

However, if you live near a marine system such as oceans you may want to be most careful with nitrogen pollution, because nitrogen is usually the nutrient in shortest supply. Therefore, adding any amount of it can cause a big increase in plant growth. 

The biggest causes of eutrophication also changes where you are because of the different human activities that take place in different locations. 

For example, in the Gulf of Mexico, farming of crops and livestock are the greatest source of phosphorus. 

However, in the Chesapeake Bay, phosphorus comes largely from stormwater runoff in cities and wastewater. Solutions to eutrophication should first focus on reducing the amount of nutrients emitted by human activities. 

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Rain can easily sweep nutrients into storm drains and nearby bodies of water

According to various studies, the main areas to focus on are agricultural impacts such as crops and livestock, pollution from energy sources such as fossil fuels, home fertilizer use, wastewater treatment, and using eco-friendly cleaning products. 

To reduce the impact of crops and livestock, we can purchase from well-managed, organic farms that are using sustainable growing practices such as using only organic fertilizers.

The impact of fertilizer isn’t limited to just farms and agriculture. In urban areas, studies show fertilizers used to keep lawns healthy is one of the biggest influences of eutrophication, since storm water can easily sweep excess nutrients away into nearby bodies of water. 

To reduce the impact of fertilizers at home, check what’s in your fertilizer and see how you can replace it with less impactful ones.

To limit the impact of energy use we can switch to cleaner fuels for example solar and wind power. The reason is that when we burn fuels, their emissions go up into the atmosphere and eventually settle back down again into bodies of water, or on land, where rainwater can easily sweep them into nearby bodies of water. 

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Power plant pollutants will eventually fall into nearby bodies of water

This is known as atmospheric deposition and while it does occur naturally, humans have significantly increased the amount of nutrients in the atmosphere. By switching to clean energy sources and lowering our energy use we can limit the impact of using energy.

One of the last ways we can limit our impact on eutrophication is to use eco-friendly cleaning products. Phosphates help with loosening stains and messes on clothing so it’s often found in many cleaning products. 

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Laundry detergent could be one of the largest causes of eutrophication in your own life.

According to one study, the biggest contributor from cleaning products comes from using dishwasher detergent. This impact can be significantly lowered by using an eco-friendly alternative. 

See our recommendation for eco-friendly cleaning products here.

After we’ve reduced the amount of nutrients we put into the environment, there are certain strategies we can use to further limit eutrophication such as filtering nutrients out of storm water and filtering excess nutrients out of bodies of water. We could also try adding oxygen into anoxic waters but again solutions should start with preventing nutrient waste in the first place.

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