Why Is Beach Water Brown?

We have come to associate clean ocean water with blue or green in color. In some parts of the world, it is crystal clear. While in other regions, it is somewhat murky. But clean ocean water is always blue or a shade of blue. Or is it? Sometimes we also see brown beach water. So why does beach water turn brown, and is it clean?

Beach water can be brown for several reasons, including plant materials, sediment, or phytoplankton. Brown beach water does not necessarily mean that the water is unclean or sewage is leaking into the water. In most cases, brown beach water is perfectly harmless and safe to swim in.

So, why is beach water sometimes brown? We have done much research to determine what causes beach water to become brown and have created a list of possible explanations below. Take note that this is not a comprehensive list, but merely some of the common reasons beach water can be brown.

Plant Materials Can Turn Beach Water Brown

One reason beach water appears brown is because of bamboo plant materials that have washed up from the deep sea. This sometimes happens if there is a storm deep in the ocean and the bamboo has come dislodged from the ocean floor.

When nearing the water, you will see bamboo particles floating in the water. These particles can be big or small. You will also notice a remarkably familiar smell. The smell of bamboo. Some people describe it as being the smell of the ocean. Bamboo particles do not smell foul, but the water will smell.

Bamboo particles are perfectly safe, and it is acceptable to swim in water discolored from bamboo. Take note; however, that bamboo does stain. Therefore, it is best to avoid swimming in the water wearing white.

The Surrounding Vegetation Turns Beach Water Brown

In some cases, the vegetation, or plants that grow around the beach, can turn the water brown. This happens when the plants leach tannins into the beach water, causing it to turn brown. While leaching never sounds good, in this case, it occurs naturally.

The tannins can be leached into the water when it rains or from streams that flow into the ocean. When plants have leached into the sea, the beach water should not have any peculiar smells. It is safe to swim in water where plants have leached into. However, brown beach water from plant tannins can also stain your clothes. So take care when swimming in this water.

Sediment Causes Beach Water To Become Brown

In some cases, sediment, or mud, causes beach water to turn brown. This often happens where rivers flow into the sea, as the mud and dirt from the river water mixes with the ocean water, turning it brown. Mud particles are tiny, so they take a long time to settle at the bottom. Therefore, the mud remains suspended in the beach water, turning the water brown.

In this case, the water should also not have an unpleasant smell. It is perfectly safe to swim in beach water that is brown because of sediment. In some cases, this water may also be warmer than the other water, as the river water temperature may be higher than the ocean water. 

Phytoplankton Causes Beach Water To Turn Brown

Many microscopic organisms live in ocean water. They are a part of the sea’s ecosystem and are vital at keeping the ocean life in balance. Some of these microscopic organisms are known as phytoplankton. Phytoplankton can accumulate and turn water into many colors, including red, orange, and even brown.

Phytoplankton needs sunlight to survive and will float up and attach to bubbles in surf foam, causing the foam to turn brown. This phenomenon is known as surf scum. Although surf scum might not look appealing, it is harmless. However, experts recommend that you don’t swim in surf scum or let your animals play in the scum.

Surf scum can appear at any time and often happens when strong winds blow the foam closer to the beach. This foam usually doesn’t last long and will typically have no smell.

Another occurrence that can cause beach water to turn brown is the presence of diatoms. Diatoms are another kind of phytoplankton, and they accumulate under particular circumstances, causing the beach water to turn brown.

Diatoms are found in areas where the ocean is high-energy and without a rocky bottom. The beach must also be four kilometers long, and there should be rip currents present. Diatoms live in the surf zone, so they require a surf zone of 150 meters or more. They also need a food source, such as plant materials washed in from the beach.

Diatoms are a natural occurrence that turns the water brown. Like surf scum, brown water because of diatoms are not harmful and are not regarded as dangerous. You can swim in brown water with diatoms, and phytoplankton signifies a healthy ecosystem.                                                                                                                

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When Should You Be Worried About Brown Beach Water?

All the reasons above are natural events that turn beach water brown. They are not harmful or dangerous. But there are several instances where you must avoid going into brown beach water. The first, and one of the main concerns, is if the water is polluted.

If there is a pipe nearby that you can see leaks pollution into the water or foul-smelling water, it is best to avoid going near that water. Human waste will likely turn water grey rather than brown, and you might see waste particles floating in the water.

However, factory pollution can also turn beach water brown and will have a pungent smell. Oil that has leaked into the ocean will also turn beach water brown or black, and you can see oil floating on the water. You should avoid going near water where oil has spilled.

If you want to determine if brown beach water is safe or not, the general rule is to judge it by its smell. For example, suppose the brown beach water smells terrible (but not like bamboo). In that case, it is best to stay clear of the water and contact the nearest ocean conservation office.


Many factors can turn beach water brown, including bamboo particles, plant tannins, sediment, and phytoplankton. However, most of the time, when beach water is brown, it is not a problem and is not dangerous.

However, if there is a clear sign of pollution, or the water has a strange or bad smell accompanying the brown color, it is best to stay clear of the water and not go near it.