Algae Invasion Turns Yellow Sea Green

— -- It's beach time as usual for people on vacation in eastern China -- despite a thick layer of green algae appearing at popular resorts.

More than 13,500 square miles of water along the Qingdao coast have been affected by the phenomenon, Chinese media reported, and it's been a recurring event since 2007.

Scientists say the plant does not pose an immediate risk to humans, but according to Algae World News, a professional web-based online news directory for algal business and information, it can prove dangerous as it decomposes and produced toxic hydrogen sulfide gas.

The Center for Disease Control writes on its website that algae is formed in response to changes in levels of chemicals, such as nitrogen and phosphorus from fertilizer, in the water.

"Algae are vitally important to marine and fresh-water ecosystems, and most species of algae are not harmful," the CDC says, but "algal blooms can deplete the oxygen and block the sunlight that other organisms need to live, and some can produce toxins that are harmful to the health of the environment, plants, animals and people."

Some scientists believe an increase in seaweed farming may be at the root of the problem, while others point towards coastal pollution as a possible cause.

According to China's national news agency Xinhua, the clean-up work at Qingdao is already underway.

It is worth noting that in 2008, Chinese authorities spent millions of dollars to clean up the beaches ahead of sailing events at the Beijing Olympic Games.