Reddish-brown waters appeared off the coast of Long Beach this past week and officials say it’s due to the algal bloom phenomenon known as red tide.

A red tide is produced when microorganisms in the water, such as phytoplankton, grow excessively in favorable environments, resulting in millions of cells in each gallon of water and a distinctive change in the water color.

In Long Beach’s most recent case, Marine Safety Chief Gonzalo Medina said the bloom, which is located in the waters off of Alamitos Beach, appeared to be caused by the recent heat wave.

The majority of red tides in California occur between the early months of spring, February and March, and late summer, August and September. The subspecies of plankton that most commonly produces red tides, dinoflagellates, tend to prefer warmer, calmer waters.

The coloration produced in the water during this event can vary as a result of which species are blooming in the water, the light intensity and the angle of the sun shining through the water.

In some instances, excessive growth of the microorganism Lingulodinium polyedra plankton can make a red tide appear as a bright blue bioluminescent light.

While not all algal blooms pose a threat, they can be considered harmful to the environment because some organisms produce toxins that can have harmful effects on people and wildlife, according to National Ocean Service. It is not clear at this time what kind of species produced the red tide or whether it poses a threat to the environment.

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