In the ocean, microscopic forms of algae, known as dinoflagellates, can "bloom" into dense patches near the surface, often referred to as "red tides." Some of these harmful algal blooms (HABs) are dangerous, producing toxins that can kill marine organisms, taint shellfish, cause skin irritations, and even foul the air. They seem to be increasing in size, intensity, and persistence—possibly due to nutrient-rich runoff from land or a warming climate. Learn more about what scientists are doing to predict and prevent harmful algal blooms.