Qingdao beach after an invasion of sea lettuce.
Many species of sea lettuce are a food source for humans in many countries. However, rotting leaves produce large quantities of hydrogen sulphide, a toxic gas. According to environmentalists, one of the main causes of this phenomenon is the excessive use of nitrates used by farmers to feed pigs. Algae use nitrates as a source of food. China is incidentally the biggest pork producer in the world (China almost produces more pigs than the rest of the world combined).
China water pollution images, water pollution in China photos