Like many other frequently asked questions we receive, there isn’t a straight answer to this question. There are various kinds of algae, and each can affect people and animals differently. Algae’s impact on humans, animals and other plants also depends on the quantity.
To determine whether the algae in your pond are potentially harmful, it’s important to first identify the type of algae. In addition, it’s always best to mitigate risks by having a professional recommend ways to minimize and control algae growth.
What Is Algae?
Algae are aquatic photosynthetic organisms, which means that they use sunlight to produce their food. They produce oxygen and are considered the base for almost all aquatic life, serving as a source of food for other organisms. Algae can be as small as one-cell microscopic organisms and as big as 100-foot-long seaweed.
Algae need sunlight, water, carbon dioxide and nutrients to grow. You can find algae growing in aquatic environments, including oceans, lakes, rivers and ponds. Some varieties can also grow on shaded, moist surfaces like under rocks and on your home’s siding.
How Does Algae Develop in Your Pond?
Algae are present in many bodies of water, including ponds. They grow through photosynthesis, capturing sunlight and converting it into energy. Algae also take nutrients like phosphorus and nitrogen from fertilizer runoff, waste and decaying organic matter in your pond.
Types of Algae and Their Characteristics
There are many algae species, often categorized by color. The primary reason algae grow in different colors is the photosynthetic pigments present. In slow-moving, warm and nutrient-rich water, algae may proliferate, causing an algal bloom.
There are three primary types of algae — filamentous, macrophytic and planktonic. Often, algae that become a nuisance are of the filamentous variety. Here’s a quick look:
- Filamentous algae:This type of algae usually grows on the bottom of the pond. As it grows, the hair-like strands interweave like a web or tangled hair to form larger mats. These mats become buoyant as they grow and photosynthesize, eventually filling with air and floating to the surface. This type of algae is prevalent in ponds and can be very unsightly. Many species of filamentous algae grow throughout the season.
- Macrophytic algae:Similarly, these algae typically grow near the bottom of a water body and resemble a vascular plant. The two common types of macrophytic algae are Chara and Nitella. However, macrophytic algae are tough to identify and often get mistaken by pond owners for other types of common aquatic plants. It almost always takes an aquatic expert to identify this type of algae.
- Planktonic algae:These microscopic algae cells float freely in the water column. At low density, planktonic algae are usually not easily visible in the water. However, when enough cells grow in the water column, they come together to form groups of green scums that resemble paint or give water that “pea soup” look.
Algae Colors
Some of the most common algae colors include red, green and brown.
Red Algae
Red algae, also known as Rhodophyta, commonly include many seaweeds and other algae forms with a bright red color. Red algal blooms get their color from phycoerythrin, a photosynthetic pigment. Red algae also contain chlorophyll-a, chlorophyll and phycocyanin. Red algae may form deeper in your pond because of their ability to absorb blue light. While some red algae are not toxic, you should always be cautious until you can identify the algal bloom. Harmful algal blooms can adversely affect marine life and may even be hazardous to humans in some cases. Despite their name, red algae are not technically algae, but their development and growth are similar to planktonic algae.
Green Algae
Green algae, often called Chlorophyta, develop in marine and freshwater habitats. Some green algae may also live in the moist soil surrounding a pond. Green algae have three types of cellular organization patterns — colonial, unicellular and multicellular. In many cases, unicellular green algae have flagella for improved motility. Colonial types of green algae include Hydrodictyon and Volvox. Some kinds of green algae, including Chlorella, are non-motile. Some blue-green algal blooms may produce toxins. Green algae are harmful to humans and to aquatic life if they are swallowed or touched. Toxic green algal blooms can create airborne droplets, which are dangerous if inhaled.
Brown Algae
Brown algae, known as Phaeophyta or dusky plants, have a brownish-yellow color due to a combination of various photosynthetic pigments, including chlorophyll-c, chlorophyll-a, xanthophylls and fucoxanthin. Many types of brown algae that form in ponds adhere to the walls with calcium. Often, brown algae survive in poor light and with few nutrients. In some cases, brown algae develop root-like structures known as holdfasts that help them anchor to the substrate. Brown algae may release toxins when they die. These can cause illness in humans and aquatic life. In general, if algae proliferate, you should avoid touching the water.
Is Algae Harmful?
Algae are a natural part of your pond’s ecosystem. They serve as a food source for inhabitants, produce oxygen that’s essential for aquatic life and support nutrient cycling. However, algal blooms can become a problem when managing your pond.
Algal blooms are one of the most common problems in a lake or pond. These rapid growths of algae can be harmful to people, animals and the environment. Algal blooms are caused by an imbalance of nutrients, sunlight and other water conditions.
Harmful Algal Blooms (HAB) can produce toxins, become too dense, use up the oxygen in your pond and release harmful gases.
Health Risks of Algal Blooms
HABs can cause a variety of mild to serious illnesses in both humans and animals. The symptoms vary depending on the type of HAB and the time of exposure. Here are some of the common health risks of HABs, according to their type.
1. Filamentous Algae and Macrophytic Algae
Filamentous algae can grow abundantly in water bodies with excess nutrients. The most significant harm these algae cause is being unpleasant to look at and causing pond odor. Filamentous algae don’t usually pose any risk to humans or animals, but overgrowth can create unsightly conditions or harbor harmful species.
However, if the look or smell of algae bothers you, our team at AEC suggests controlling the growth of algae to make water recreation more appealing for you and anyone else who uses it. Algaecides registered with the Environmental Protection Agency (EPA) can control most of this type of algae. Similarly, macrophytic algae can occasionally grow to nuisance levels but are not a cause of concern for the safety of animals or humans.
2. Planktonic Algae
Planktonic algal blooms are dangerous because they can plague anything from small ponds to large lakes with excess nutrients. Most species of this algae do not pose a threat to organisms. However, some planktonic algae species produce harmful toxins that can affect humans and animals. The most common toxin causing recent concern is microcystin, a group of toxins produced by several species of cyanobacteria.
Cyanobacteria, better known as blue-green algae, can accumulate in ponds and lakes when conditions are ideal and blooms occur. Blue-green algae can be harmful when they produce microcystin toxins.
3. The Microcystin Toxin
The microcystin toxin has several negative health effects on the human body, including affecting the liver and gastrointestinal system. Acute symptoms can include nausea, vomiting, fever and skin rashes. Consistent exposure can even lead to potential long-term effects, especially for people with preexisting liver conditions.
People have reported a wide range of microcystin concentrations in lakes and reservoirs, ranging from nondetectable to upward of 10,000 micrograms per liter (µg/L). When the microcystin toxin is present, it can cause concentrations from <1 to 100 µg/L, depending on the specific algae present and the cell density.
Guidelines for safe levels regarding the recreational use of water containing microcystins are as follows:
- Levels above 6 µg/L trigger a public health advisory. People should not swim or wade, swallow water or touch surface scum.
- Levels above 20 µg/L trigger a no-contact advisory. It is recommended that the public avoid all contact with the water.
The EPA has recommended a microcystin level of 8 µg/L or less for recreational water use. However, not all states have set guidelines for the recreational use of water containing harmful toxin levels. We hope and expect to see more state water safety directives in the future. For now, if you see a bloom in the water and want to be cautious for pets, children and yourself, we recommend following the adage, “Better safe than sorry.”
What to Do if There’s Algae in Your Pond
Managing algae is a key maintenance task for pond owners. If you notice algae growing in your pond, the best solution is to rely on a professional to manage and control it with targeted treatments. AEC is your trusted expert for pond and lake management services. We have the equipment, knowledge and years of experience to treat harmful algae so you can enjoy your pond.
Contact AEC About Algae Control for Your Pond
If your pond has a large buildup of algae or you suspect that you may have toxic algal blooms, contact AEC today for a consultation with one of our pros on a custom pond management plan. Call us today or request a consultation online.
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