Over 20,000 wetsuits & accessories in stock today!

Secure Checkout

What Is Red Tide?

   August 22nd, 2019   Posted In: Articles  

What Is Red Tide? Everything You Need To Know About Toxic Algal Blooms

Let’s start with the facts: Red Tide is a common term used to describe the naturally-occurring phenomena of algal blooms, which occur in the ocean and sometimes cause the water to appear red in color. There are multiple reasons why the name “red tide” is a misleading misnomer and being phased out by those in the scientific community.

Why The Term Red Tide Is Misleading

  1. The phenomena of a “red tide” may not turn the water red. It may not affect the color of the water at all.
  2. Harmful algal blooms are not affected by the tide or movement of the ocean water.
  3. The term “red tide” over-simplifies the occurrence of algal blooms, which can actually be caused by several different species of algae in the group known as bloom-formers.

To be more precise, we will refer to these occurrences as “harmful algal blooms.”

What Is An Algal Bloom?

An algal bloom is a large concentration of aquatic microorganisms caused by an increase in nutrients and rapid multiplication of algae. Not all algal blooms are harmful: they occur worldwide and are part of a natural cycle in many regions of the planet. In fact, many algal blooms are beneficial, creating an abundance of food for ocean-dwelling animals.

Harmful algal blooms can occur in oceans, bays, and estuaries, but never in freshwater environments. These blooms can be caused by the presence of a wide variety of dinoflagellates (like plankton) and diatoms (microalgae) in high concentrations. These species often contain photosynthetic pigments that vary in color from brown to red and, if found in high enough concentrations, their presence can alter the coloration of the water in which they are found.

What Causes Algal Blooms?

what is red tide

Beware of this sight in water! Image courtesy of nbcnews.com.

The creation and severity of an algal bloom depend on many factors including wind patterns, temperature, nutrient levels, and salinity. While research is still under way to better understand the causes of algal blooms, scientists are getting closer to understanding just how favorable conditions align to produce such an over-production of algae in a given area. In general, algal blooms are caused by changes in sea currents, increases in water surface temperature, and an accumulation of nutrients near the ocean’s surface.

Human Activity

One suspected culprit contributing to algal blooms is… humans! Like many environmental issues, algal blooms can be traced back to human interference; in this case, from fertilizers. When rain runoff collects fertilizer from our lawns and farmlands, it eventually makes its way to the ocean. This fertilizer is rich in nutrients like phosphorus, nitrogen, and carbon: all food that algae love. This influx of nutrients allows algae to grow and reproduce rapidly. More food means more algae.

Natural Phenomena

Algal blooms have also been linked to naturally-occurring events such as slow water circulation, unusually high temperatures (climate change anyone?), and extreme weather events such as hurricanes and floods.

What Makes Algal Blooms Harmful?

If algal blooms are naturally-occurring and produce food for marine life, what’s the big deal? Why does the term “red tide” emote feelings of dread and fear?

The problem with algal blooms is that while some are beneficial to the ecosystem, some species of algae produce harmful toxins that can cause sickness and even death in both marine life and humans. During a bloom, these toxins accumulate at dangerous levels.

How do people or animals get sick?

There are several ways harmful algal blooms can affect both people and animals. Water sports such as swimming, kayaking, and fishing can bring humans into contact with the contaminated water. Breathing in contaminated water droplets, mist, or sea spray can have adverse effects. Eating contaminated seafood like fish or shellfish can lead to serious illness or even death.

How do I prevent getting sick?

You cannot tell if an algal bloom is harmful just by looking at it, so it’s best to err on the side of caution. If you see an accumulation of algae or suspect an algal bloom is occurring, keep yourself and your pets out of the water. If you do come into contact with a large number of algae, wash yourself off as soon as possible with fresh water. Try to keep your pets from licking themselves until they have been rinsed. Before visiting a beach, check the local water conditions. State and local health departments usually have up-to-date information regarding water safety.


Symptoms of adverse effects caused by harmful algal blooms vary widely. The diverse species that cause these blooms produce different compounds that affect the ecosystem (and your body) differently. Symptoms related to harmful algal blooms include:

  • Skin, eye, nose, and throat irritation
  • Headache
  • Neurological symptoms
  • Abdominal pain
  • Vomiting
  • Diarrhea

Algal Blooms On the U.S. Coasts

Where and when do these harmful algal blooms occur? All coastal areas of the United States have experienced harmful algal blooms, even Hawaii and Alaska, but some areas are more prone to these blooms than others. Blooms are much more likely to occur during the summer months when the surface temperatures of the water are likely to be higher.

Gulf of Mexico

Karenia Brevis is the dinoflagellate responsible for the majority of algal blooms in the Gulf of Mexico. These blooms have been documented for almost 200 years and occur annually along the west coast of Florida, often reaching all the way to the east coast of Mexico.

Gulf of Maine

Another area that experiences frequent algal blooms is the coast of Maine. Here the likely culprit is Alexandrium fundyense. These blooms can negatively impact the fisheries in this area, rendering the shellfish inedible for many weeks.

More Research on Red Tide

Though a naturally-occurring phenomenon, algal blooms are developing at an increasing rate as average sea temperatures rise and humans continue to dump contaminants into the oceans. As much as we know about harmful algal blooms, more research still needs to be conducted to better understand their root causes and potential effects. Only once we better understand these events can we begin to offer steps to mitigate the occurrence of harmful algal blooms.

Taylor is a former marine mammal trainer and zookeeper who quit her job to spend more time with her dog, Dobby doing water activities like SUP and kayaking. She spends her time freelance writing from somewhere in the woods and lives out of her converted campervan when she isn't out exploring the wilderness. She is also PADI certified.

Latest Posts by Taylor Ritz (see all)

Leave a Reply

Your email address will not be published. Required fields are marked *