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

Q: Let’s start by talking about what an environmaental scientist is and why you chose 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 uses the tools of biology, chemistry, and engineering to solve or reverse this damage.

I am the second kind. I needed to have a purpose. If you can’t fix the problems you see, it’s very hard to stay 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: Most of our freshwaterabout 70 percentgoes to agriculture. Water runoff from farms is one of the biggest water pollutants on Earth. Yet, we need farms because they provide us with the food we eat. That problem started to roll around in my head because we’re not only talking about clean water, we’re also talking about feeding 10 billion people. 

Agricultural wastewater contains high quantities of nitrogen and phosphorus. These nutrients are found in fertilizer and animal manure. When they seep into lakes and oceans, they can cause dead zones.


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

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

A: A dead zone is a low oxygen zone in a river, lake, or ocean where nothing can live. [Excess] nutrients from agricultural wastewater cause microalgae to grow quickly. Microalgae are tiny plants that live in the water. Like regular plants, microalgae use photosynthesis to absorb sunlight and carbon dioxide and turn it into oxygen.

When you add nitrogen and phosphorus to the water, microalgae absorb these nutrients. They quickly grow into a biomass known as an algae bloom. Algae blooms turn the water green or red, depending on the strain of
the microalgae.

Having so much microalgae in the water is not the harmful thing. The problem starts when these microalgae die. The bacteria that decompose the microalgae absorb 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 that I wanted to find a way to upcycle wastewaterto make wastewater reusable. I realized we could use microalgae to clean water polluted by agricultural waste.

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

A: I learned aquaculture produces a lot of wastewater. Most fish farmers grow fish in human-made ponds. The fish in these ponds produce so much poop that farmers need to replace all the water in each pond every day. The wastewater they remove from these ponds drains into tributaries, 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 asked farmers to tell us all about fish farming and learned that 70 percent of their expenses go into feeding their fish. So if there was a way to make fish food cost less, they would be interested.

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

1,000 km2
10,000 km2

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