Algae bloom is caused unnecessary amounts of increased nutrients in the water or from higher temperatures. Increased nutrients may come from human interactions such as agricultural runoff, factories, etc. Climate change has also a huge affect on algae bloom, for it allows it to flourish due to the higher temperatures. 

Algae can cause devastating damages to marine life and humans too. Florida in the past have had 100s of million dollars worth of damages due to algae bloom. Algae bloom can reduce the oxygen level in waters, and therefore killing the animals by intoxicating them. When consumed by other animals or humans, the toxins can be inhales by humans, sickening humans and animals.

The San Francisco Bay has had this problem for decades. Each year, it kills 10s of thousands of fish and wildlife. 

Due to California's recent burst of heatwaves and high temperatures, algae blooms will continue to thrive. More and more damage is being done because of climate change and higher temperatures. 

Credits: https://www.newsweek.com/california-algal-blooms-dangerous-toxins-killing-fish-1739915