Blue Green Algae Monitoring Department of Water Resources (DWR) environmental scientists continue to monitor for blue-green algae and their toxins within the Oroville-Thermalito Complex. Monitoring occurs during the summer months with water samples taken at various locations regularly, which are sent to a lab for toxin analysis. There are currently no harmful algal bloom (HAB) advisories for Lake Oroville, the Thermalito Forebay, or the Thermalito Afterbay. Blue-green algae (cyanobacteria) is a natural component of ecosystems. Under certain conditions, including warmer temperatures and increased nutrient loads, algae can grow rapidly causing “blooms.” Algal blooms sometimes produce toxins that can be harmful to people and animals. Algal blooms can make the water appear green, blue, or brown in color.