"I didn't even have 20 centimeters of visibility. It was terrifying: I lost track of where the surface was and where the seabed was. Even the characteristic decomposing smell of red tide was such that it was impossible to breathe naturally. Either way, I had to inspect the situation since there were dozens of dead species floating at different depths," says Vanopdenbosch, the project director of Innoceana's Marine Education and Conservation Center (MCEC).

The situation occurred within the framework of one of their marine conservation expeditions in the South Pacific region. The participants —in this case from Argentina, Mexico, the Netherlands, and the United States— were startled to see the tragic scene of destruction.

Red tides are caused by a bloom of microscopic red algae called dinoflagellates and occur primarily because of high levels of nitrates and phosphates reaching the ocean. Generally, these minerals are nutrients from agriculture and, above all, from pesticides and fertilizers. When rains increase, the rivers carry these nitrates and phosphates into the sea, creating a breeding ground for algae, promoting their exponential growth and excessive blooming. Climate change must be added to this cocktail of elements: warmer currents and thermoclines are a favorable environment for algae proliferation.

Even though red tides have been around for years and may have natural causes, they are now occurring with worrying frequency. Using pesticides, fertilizers, and heavy chemicals in Costa Rica has very negative consequences. Other practices that increase the presence of this phenomenon are constructions with unsustainable methods that provoke sediment and fluvial erosion.