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

(N/A) Algal bloom:
Algal bloom refers to an excessive increase in the population of algae or blue-green algae in a water body,which causes the water to become discolored. This process leads to a significant increase in the biological oxygen demand $(BOD)$,which depletes dissolved oxygen,ultimately resulting in the death of fishes and other aquatic organisms.
Red-tides:
Red tides are caused by the rapid multiplication of red dinoflagellates,such as $Gonyaulax$. Due to their massive numbers,the sea surface appears red in color. These organisms release large amounts of toxins into the water,which can be lethal to a large number of marine animals,including fishes.