Karenia brevis is a single-celled organism known as a dinoflagellate. It is primarily found in warm coastal waters, particularly in the Gulf of Mexico. This organism is notable for its ability to produce toxins that can harm marine life and humans. When conditions are favorable, Karenia brevis can multiply rapidly, leading to harmful algal blooms, commonly referred to as "red tides." These blooms can deplete oxygen in the water and release toxins that affect fish, shellfish, and other marine organisms, posing risks to both wildlife and human health.