Red tide is a phenomenon caused by the rapid growth of certain types of algae in the ocean, particularly dinoflagellates. These algae can produce toxins that are harmful to marine life and can affect humans who consume contaminated seafood or come into contact with the water. The term "red tide" refers to the discoloration of the water, which can appear reddish or brownish due to the high concentration of algae. While not all algal blooms are harmful, those that are can lead to fish kills, respiratory issues in humans, and other ecological problems.