Major Causes of Contamination: Commercial Tilapia Farms

Hydrilla growing around a commercial tilapia farm in Santiago bay

Why are tilapia farms allowed to contaminate the lake?

Lake Atitlán is a 'Protected Area' under Guatemalan law, but commercial tilapia farms are being allowed to operate on the lake, even though all the nutrients that they leave in the lake are accelerating the destruction of its ecosystem.

There are six commercial tilapia farms in Santiago Bay alone. Like all intensively fed fish, farmed tilapia produce fecal waste and other waste such as uneaten food, causing nutrient enrichment in the water. Exactly how many excess nutrients are added to Lake Atitlan every day by these operations, and how quickly are they accelerating the collapse of the lake's ecosystem?  It's impossible to know exactly. We also don't know who owns the farms and what powerful (dangerous) connections they have.

We do know that there are tens of thousands of tilapia and that tons - literally boatloads - of commercial fish food are taken to the farms each week, and that these tons of fish food are then converted into highly bioavailable nutrients (phosphorus). And we know that the farms are operating with impunity in a so-called Protected Area.

The tilapia farm in the photograph here is in an unusually shallow area. The lake has responded with an immense hydrilla bed to consume the nutrients, but it will only consume a small fraction and the rest will flow into the open water on the other side of the farm. Most of the farms are in water that is too deep for weeds to grow.

Recommended reading

Dr. Jeffrey McCrary spent ten years studying how a small tilapia farm which only existed from 1995 to 2000 degraded Lake Apoyo in Nicaragua. “One small cage screwed up the entire lake — the entire lake!” he says. "Waste from the cages polluted the pristine ecosystem, and some tilapia escaped. Charra, an important aquatic plant food for fish, disappeared, leaving the lake a wasteland. Today, some species of plants and fish are slowly recovering, but others are probably gone forever."