Harmful Algal Blooms (IMAGE) Florida Atlantic University Caption Harmful algal blooms occur when colonies of algae — simple plants that live in the sea and freshwater — grow out of control and produce toxic or harmful effects on people, fish, shellfish, marine mammals and birds. Credit FAU Harbor Branch Oceanographic Institute Usage Restrictions Credit: FAU Harbor Branch Oceanographic Institute License Original content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.