What Caused Your Pond Water To Go Blue

The disruption in your pond’s ecosystem could turn the crystal clear water a distinct blue color. Knowing what caused your pond water to go blue and what you can do about it is important, especially if it’s caused by an algal bloom that needs to be fixed quickly.

Pond water may be naturally blue due to increased light scattering from suspended particles, minerals in the water (such as calcium carbonate, copper, or aluminum), or from blue green algae. The most common cause for your pond water to go blue, especially when the temperature increases, is caused by toxic blue green algae.

In this article, we will cover what can cause your pond water to go blue. We’ll discuss both natural and artificial sources for this blue coloration. We will also discuss how to make your pond water crystal clear again, and what blue pond dye does and if it’s harmful.

Healthy Pond Color

There are several elements that influence our perception of water’s color. Particles in water, for example, may absorb, scatter, and reflect light. When we stare down into or through a big volume of water, the blue hue becomes visible.

Most pond owners in the United States prefer the aesthetics of crystal-clear water so they can view and appreciate their lovely fish. In reality, the most crystal clear water has an inherent blue hue that results from its molecular structure and activity.

The good news is that keeping your water pure and clear is quite simple. It does not require the use of harmful chemicals. But first, let’s figure out the causes of blue pond water.

Natural Causes Of Blue Pond Water

Around 75% of the planet’s surface is covered by water. A lot of people believe blue represents clean lakes, ponds, and oceans. But water isn’t always naturally blue.

The blueness of water can be generated by the scattering of light from suspended particles, minerals in the water, or from blue-green algae.

1. Light Scattering

Light scattering occurs in water when the light particle hits a suspended particle in the water, which can make the water appear blue. This may be more noticeable after it rains heavily as the increased runoff and input of sediment to your pond can, in turn, scatter more light.

2. Minerals

Minerals such as calcium carbonate, copper, or aluminum entering your pond water can give it a blue color.

Transparent water with a low concentration of dissolved minerals appears blue.

Calcium carbonate comes from rocks like limestone. It is actually white, but these white minerals reflect and refract whatever color the water is already. So, if the water is slightly blue, calcium carbonate in the water may make it appear MORE blue.

Copper can also give water a cloudy to blue-green appearance at high concentrations. Many rocks, such as chalcopyrite, contain copper which can quickly turn your pond blue. Exposure of copper to air and water and will cause it to corrode, so you may notice a color change almost overnight, especially after a heavy rain.

Aluminum in water naturally reflect and refracts sunlight and gives it a vivid blue color. An example of this is the famous Shirogane Blue Pond in Japan that receives water from a waterfall that flows over aluminum-rich rocks turning the water a stunning blue hue.

3. Blue-Green Algae

Overall, the most likely cause of your pond turning blue is Blue-green algae.

The blue coloration occurs when the accumulation of the blue-green algae cells are high enough that they discolor the water. This is also called a bloom.

These blue-green algae (Cyanobacteria) blooms are caused by cyanobacteria, a type of bacteria capable of photosynthesis, and are commonly known as toxic algal blooms.

They not only color the water blue, but can produced bad odors, form scums, affect fish populations, and reduce the quality of the water.

Excess nutrients are one of the primary causes of algal bloom. Algae, like terrestrial plants, require nutrients such as nitrogen and phosphate to flourish.

Nutrients from fertilizers, animal manure, sewage treatment facilities, and other sources can be carried by water runoff from land. When excess nutrients wind up in a pond or lake, they encourage algae development especially when the water is warm, resulting in an algal bloom.

Effects of Blue-green algae

When blue-green algae multiply quickly, they form blooms that look like scum on the surface of a pond and can affect the color of the water. When a big cyanobacterial flower fades, the water may appear clean. 

Additionally, high algal growth remains suspended in a body of water. It can block light and deplete dissolved oxygen, resulting in a eutrophic situation. As a result, it can dramatically decrease all life in the body of water.

Toxins from blue-green algae can harm the liver or neurological system of animals. Medicines can treat the damage to the liver, but the damage to the neurological system subsequently results in death.

Crystal Clear Pond Water

In healthy aquatic habitats, algae are usually present in low numbers, and the water appears clear. The most straightforward approach to avoid the difficulties caused by cyanobacterial blooms is to prevent them from occurring in the first place. Eradication of algae can be accomplished by lowering nutrient input into the water supply, such as phosphates, or by aerating the water.

Step 1: Remove Debris

The first step is to keep trash and bottom sludge to a minimum. Especially if you have many nutrient‐rich material runoffs. Cleaning up deposits with a pond vacuum or wide-brim pond net is an excellent way to tackle the problem.

Pond vacuums are a perfect choice for more extensive ponds. Since they clean considerably faster, an average pond net can help scrape the pond floor. Also, it can remove tiny amounts of bottom muck if you have a small pond.


After you’ve removed a significant amount of sludge, you’ll want to try to keep the debris from accumulating again in the future. By skimming the surface with rakes or nets, you can avoid adding more nutrients to the pond while eliminating rotting material. Pond owners should use fine mesh in netting to collect the most waste. Additionally, a skimmer should have a large leaf basket to make maintenance easy.

Step 2: Reduced Sunlight

Make shelter for your pond if it receives too much sun. Plants such as water lilies can be added if there is enough room. Growing trees or tall shrubs around the pond or covering it for an extended period with opaque plastic fabric can also assist in reducing algae development. This will give quick shade, assist in cooling the water, and absorb nutrients.


Another prevention is to reduce the amount of sunlight accessible to blue-green algae by spreading a thin layer of wheat straw across the pond’s surface to shade the algae and reduce the extent of the algae bloom.

Step 3: Aeration System

Algae grow in water with low oxygen levels. Adding an aeration and circulation system to the pond or Installing a waterfall, fountain, or aerator to agitate the pond top and assist release gases such as CO2 can give your pond an immediate boost. This also allows the water to absorb more oxygen, which will help minimize the prevalence of algae in a short period.


A few long-term methods for preventing blue-green algae include adding solar-powered aerators to keep the water in the pond moving. The addition of an aerator or fountain will aid in the removal of excess nitrogen. Also, aeration in water enhances the flow of water around the pond.

Step 4: Blue Pond Dyes

Blue pond dye is mainly used to prevent the growth of rooted aquatic vegetation and is effective on plants. If the pond owner doesn’t mind the artificial blue tint, it’s beneficial for controlling nuisance algae and submerged aquatic vegetation.

Blue water ponds are common in Utah and are the consequence of blue pond dyes.

However, blue pond dye is most effective on plants in their early stages and grows below 18 inches from the surface. For instance, Pond dye is effective for  Filamentous blue, green algae that require less light and is over 18 inches deep.

Is Blue Pond Dye Bad?

Blue pond dye is undoubtedly a short-term solution for decreasing algae and preserving your natural pond during the spring and fall seasons. But it can also be used for near-immediate relief for unhealthy ponds all year-round.

Aquatic dyes provide a blue or blue-green hue to the water when used as a shade in the summer to minimize excessive sunlight penetration and decrease development by inhibiting photosynthesis.

The following are some of the advantages of blue pond dye:

Cool Down The Pond

Blue pond dye adds a blue or blue-green hue to the water, darkening it. The blue hue lowers sunlight penetration and stops excessive sunlight from shining through.

It helps to deflect the sun’s rays, keeping the water temperature lower, especially during the warmer months. Cool water has more oxygen than warm water, making it healthier for the fish and beneficial microorganisms in the pond.

Reduces Algae Growth

Algae love to be in the sun. To assist limit the excess algae development, you can add a non-toxic color to the water. The blue pond dye works by absorbing UV radiation. As a result, if the quantity of sunlight entering the pond is low the algal development will not flourish.

Protects The Aquatic Life

There is a widespread perception that utilizing any kind of chemical or artificial coloring might be harmful. Blue pond dye will not damage any aquatic life in your pond in this situation. This is no doubt a tremendous benefit. Pond dye also helps fish blend in with their surroundings, making them less noticeable to birds and other predators.

Will Not Kill Your Pond Plants

Aquatic dyes are not herbicides, and expecting them to destroy all the vegetation in your pond is a misconception. While dyes are not harmful to fish or other marine creatures, they can impact attractive submerged plants that fish and different aquatic life may utilize for food and shelter.

Russell Singleton

Russell has a Bachelor of Science (Environmental and Marine Geoscience) with Class I Honors. He is currently completing his doctorate in science and is passionate about all earth processes, especially isotope geochemistry and paleohydrology.

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