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 and how people affect it. The first kind just study and observe. The second kind try to reverse the damage people do. They use the tools of biology, chemistry, and engineering.

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

Q: What environmental problem did you want to focus on?

A: About 70 percent 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. We’re not only talking about clean water. We’re also talking about feeding people.

The wastewater from farms has a lot of 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. These tiny plants absorb sunlight and carbon dioxide and turn it into oxygen.

When you add nitrogen and phosphorus to the water, microalgae absorb them. They grow into a biomass known as an algae bloom.

Microalgae itself is not harmful. The problem starts when these microalgae die. The bacteria that decomposes the plant absorbs a lot of the oxygen from the water. This causes a dead zone.

algae, as seen under a microscope

algae in water

Q: How did you decide to tackle this problem?

A: I decided to find a way to upcycle wastewater and make it reusable. I realized that microalgae could clean water polluted by agricultural waste.

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

A: Most fish farmers grow fish in human-made ponds. The fish in these ponds produce so much poop that farmers need to replace the water every day. The wastewater drains into tributaries and 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 70 percent of their expenses go into feeding their fish.

A man feeds fish at a fish farm.

And that was your aha! moment. You had two environmental problemsaquacultural waste 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

 1000 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 aquatic animals. This cycle can lead to the creation of dead zones. There are more than 500 dead zones worldwide.