Find out what do the terms 'algal bloom' and ‘red tides' signify. 

Explanation

Presence of large amount of organic nutrients in water causes excessive growth of planktonic or free floating algae called algal bloom.
Due to this colour of water bodies get changed.
This may cause deterioration of the water quality and fish mortality.
Water hyacinth (Eichhornia crassipes) is the world.s most problematic aquatic weed.
They are introduced into India for their beautiful flowers that have caused havoc by their excessive growth by causing blocks in our water bodies.
This weed is commonly known as .Terror of Bengal..