What do septic tanks have to do with a massive seaweed bloom? Researcher: ‘It’s like Jaws. You got to cut the food supply off.’ Updated: What do septic tanks have to do with a massive seaweed bloom? ORLANDO, Fla. – Researchers blame rising temperatures, fertilizer runoff and increasing nitrogen levels from old septic tanks for a growing bloom of seaweed that made its way to Central Florida. The piles of seaweed washed up on the shores of Brevard, Volusia and Flagler counties in May, and it was so thick in some places that shovels were no match for it. “In your mind, you have this pristine beach that you see in all the pictures of Florida, and then you see this, and it’s like, ‘That’s not what I expected,’” said Andy George, who was visiting Cocoa Beach with his wife, Melanie.