Red tide is caused by

Algal blooms are the cause of red tide. 

The oxygen level of the water is reduced as a result of the algal blooms. 

Karenia brevis, a minute algae, is responsible for the disease, which can kill enormous numbers of fish and other sea life, including dolphins and manatees, as well as make shellfish deadly to humans. K. brevis generates toxins that can irritate the respiratory system. 

Red tide can irritate the skin.

So, option C is the right answer.

Option C : Algal blooms.