Marissa Cuevas Flores is the founder and CEO of microTERRA based in Mexico.

Q: Let’s start by talking about environmental scientists. Why did you choose to become one? 

A: There are two kinds of environmental scientists. Both kinds study the environment to learn how it behaves. They also want to learn how [people] 
affect it.
The first kind just study and observe. The second kind try to fix the damage people do.

I am the second kind. I needed a purpose. I try to fix the problems I see. For me, science has always been the greatest tool that human beings have.

Q: What environmental problem did you want to solve? 

A: Most of our freshwater goes to agriculture. Water runoff from farms causes pollution. Yet, we need farms to provide the food we eat. That problem bothered me. Wastewater from farms has nitrogen and phosphorus. These nutrients are found in fertilizer. They can cause dead zones in lakes and oceans. 


Each year, 200 million tons of fertilizer are used worldwide on our crops. Yet, there is more than crops can absorb, and it is washed away by rain or irrigation.

Q: What is a dead zone? How can agricultural wastewater cause it?

A: A dead zone is a low oxygen zone in a river, lake, or ocean. Nothing can live in it. The nutrients from the wastewater cause microalgae to grow quickly. Like all plants, microalgae give off oxygen. Microalgae also absorb the nutrients from wastewater. Then they grow into a biomass called an algae bloom.

When microalgae die, bacteria decompose these plants. The bacteria also absorb oxygen from the water. This causes a dead zone.

algae, as seen under a microscope

algae in water

Q: How will you tackle this? 

A: I found a way to upcycle wastewater and make it reusable. I learned that microalgae could clean water polluted by this waste.

Q: You started looking at fish farms. What did you learn? 

A: Most fish farmers grow fish in human-made ponds. The fish produce so much poop that the water must be changed every day. The wastewater drains into rivers and oceans.

Fish farms must manage their waste problems as well as keep their fish fed.

Q: What else did you learn from the fish farmers? 

A: We learned that feeding their fish is very expensive. 

A man feeds fish at a fish farm.

So, you had two big problemswaste and fish farmers needing cheaper fish food. That’s when you created your company, microTERRA. 

Dead zones

Location and Size 

(in square kilometers)

size unknown
1 km2

10 km2

100 km2

1,000 km2
10,000 km2

Excess nutrients can lead to too much algae. Algae can block light that other plants need to grow. When algae die, they decay. Then oxygen in the water gets used up. Low oxygen levels kill water animals. This can lead to the creation of dead zones. There are more than 500 dead zones worldwide.