Red tides occur when a population of algae increases quickly in ocean waters. Some algae can produce toxins that poison animals.
Nutrients in a lake or pond build up over time, causing an increase in the amount of algae. An accelerated rate of eutrophication can lead to the deaths of many organisms in the lake or pond.
Algal bloom - The rapid growth of population of algae.
Red tide - An algal bloom that occurs in salt water.