"Water bloom" is a natural ecological phenomenon in fresh water, which is only caused by algae, such as cyanobacteria (strictly called cyanobacteria), green algae, diatoms and so on. That is, eutrophication of water body. When "water bloom" occurs, the water is blue or green. This phenomenon of "water bloom" in nature has been recorded in the ancient history of China. They quickly disappeared in nature, causing no harm to aquatic animals and humans. The so-called "water bloom" is a phenomenon in which algae multiply in large numbers in water, and the water body is blue, green or dark brown, which is the characteristic of eutrophication. The phenomenon of "water bloom" is mainly due to the fact that after wastewater containing a lot of nitrogen and phosphorus in life and industrial and agricultural production enters the water body, algae multiply in large numbers and become the dominant population in the water body.

"Water bloom" mainly occurs in still water bodies, especially fish ponds and stagnant Neijiang. The appearance of "water bloom" has a great influence on fish, which often leads to the gradual decrease of fish production and even a large number of deaths. It poses a threat to the safety of drinking water, and drinking this water for a long time is not good for human health.

After the eutrophication of fresh water, "water bloom" appears frequently, the area expands year by year, and the duration is prolonged year by year. Taihu Lake, Dianchi Lake, Chaohu Lake and Hongze Lake all have "water blooms", and even flowing rivers, such as the Hankou section of the lower reaches of the Hanjiang River, the largest tributary of the Yangtze River, also have "water blooms". The biggest harm caused by freshwater blooms is that drinking water sources are threatened. Microcystins affect human health through the food chain. The secondary metabolite of cyanobacteria blooms, MCRST, can damage the liver and promote cancer, which directly threatens human health and survival. In addition, the filtration device in the waterworks is full of algae, which floats on the water surface and affects the landscape, and there is an unpleasant smell.

"Red tide", commonly known as "red ghost", is also known as "harmful algal bloom" internationally. One or several kinds of plankton in the ocean explosively reproduce or gather in a high degree under certain environmental conditions, causing seawater discoloration, affecting and endangering the normal survival of other marine organisms, which is a catastrophic marine ecological anomaly. When a red tide breaks out, the seawater will appear different colors, such as red, yellow and green, due to the different species and quantities of red tide organisms. A large number of studies at home and abroad show that marine phytoplankton is the main organism that causes red tides. There are more than 260 species of marine phytoplankton in the world that can form red tides, of which more than 70 species can produce toxins. Some toxins secreted by them can directly lead to a large number of deaths of marine life, and some can even spread through the food chain, causing human food poisoning.

Red tide is a harmful ecological phenomenon that some phytoplankton, protozoa or bacteria in seawater proliferate explosively or gather highly under specific environmental conditions, causing discoloration of water body. Red tide is a historical name, not necessarily red, but actually a general term for many red tides. According to the causes, types and quantities of red tide, water will appear different colors, such as red or brick red, green, yellow, brown and so on. It is worth pointing out that some red tide organisms (such as Gymnodinium, Gymnodinium, Pyrodinium, etc. Sometimes it doesn't make the sea water appear any special color.