You may be looking for the word "Algae" That is the stuff that "Blooms" then decays and poisons the water which causes fish kills.
algae
A harmful algal bloom (HAB) caused by dinoflagellates that leads to fish kills is commonly referred to as a red tide. Dinoflagellates produce toxins that can affect marine life, including fish, by disrupting their nervous system and causing respiratory distress, ultimately leading to fish kills. Monitoring and managing red tides are essential to protect marine ecosystems and public health.
An algal bloom can cause harm to a body of water by depleting oxygen levels, blocking sunlight from reaching other aquatic plants, and releasing toxins that may be harmful to fish and other organisms. This can disrupt the ecosystem, leading to fish kills and impacting water quality.
Some what, yes other reasons are possibly people are dumping toxic wast into the water witch kills the fish, or there is too much fishing in one area.
The affect on redtide is it kills many fish and contaminate shell fish such as clams, mussels, which eat the algae and then poison the other organisms that eat them. Such as fish, marine birds and even humans. The algal bloom also reduces oxygen levels in the water, which further contribute to fish kill.
Excessive organic matter, especially decaying matter, can build up to toxic levels and kills freshwater fish. An example would be uneaten food or feces breaking down.
Phyllum is not used itself ,but members of this Phyllum are much important in producing red tides and bloom in sea as in red sea . These blooms are toxic to fish and other organisms+
Anything described as toxic would by definition be capable of causing death.
it kills animals in the water.
Yes, formalin kills fish.
Fish - 1977 Love in Bloom 2-15 was released on: USA: 9 February 1978
The commonest cause of a fish kill is an Aerobic Bacterial bloom. The sequence is commonly caused by firstly high amounts of runoff carrying fertilisers to the river caused by high rainfall or storms. This supply of extra plant food encourages algaes to form and bloom. These algaes then use up this excess food, bloom and die. Aerobic bacteria are then needed to decompose the dead algae and the oxygen demand of the bacteria depletes the oxygen in the water resulting in a fish kill.