Spikes of sargassum were first recorded in the Greater and Lesser Antilles (including Trinidad and Tobago) in 2011 and 2012. The problem appears to have begun many miles away. In recent years, the Amazon basin has experienced some of the world’s highest rates of deforestation. And without vegetation to hold soil in place, rain washes that soil and whatever it contains into streams and rivers. So when the Amazon basin saw greater than normal amounts of rain in 2011 and 2012, unusually high levels of nutrients such as nitrogen and phosphorus washed into Atlantic waters around the mouth of the Amazon River off the north coast of Brazil. Sargassum passed through this nutrient-rich water and responded by growing like, well, a weed. Ocean currents carried it from there to the Lesser Antilles and western Caribbean.