A Photo Guide to Identifying Types of Pond Algae

Algae, also known as phytoplankton, is present in all ponds and lakes. Between 30,000 and 150,000 species of algae are thought to exist. Some are so small that they can’t be named without a microscope.

Algae can appear in a number of different forms, colors, and quantities. Algae serves an important function in every ecosystem, but can become a nuisance when left unattended to. It’s good to know that there are several ways to stop algae from growing in your pond or other water feature at home.

In this article, we cover the most common types of pond algae and all their identifiable characteristics.

As a pond owner, being able to recognize different types of algae is an important skill. While some algae varieties are beneficial or harmless, others can take over and damage your pond’s ecosystem. The best way to identify pond algae is through pictures and descriptions of their key visual characteristics.

In this article, we’ll go through photos and details on the most common types of algae found in ponds. Learn to discern good algae from bad, and harmless algae from destructive. With this handy pictorial guide, you’ll be able to spot and manage algae in your pond.

Green Algae

Green algae, or green pond scum, is probably the most common type of algae in ponds. This umbrella term refers to a wide variety of microscopic, free-floating algae that all contain chlorophyll, giving them a green color.

When populations of green algae bloom, they collectively tint the water a soupy green. Excessive green pond algae can block sunlight and reduce oxygen for fish. However, in normal amounts, these algae are a natural part of pond ecosystems.

Identifying Features:

  • Green coloring in water
  • Suspended throughout water column
  • No rooted structures
  • Microscopic; individual algae not visible

[Photo of green pond water]

Filamentous Algae

Filamentous algae, also called hair algae or pond moss, feature long strands that resemble wet hair or string. The strands anchor to surfaces and wave in the water. Overgrowth looks like thick mats of green material across the pond’s surface.

While unsightly, filamentous algae generally doesn’t harm wildlife. However, in excess it can choke out other plants and deplete oxygen as it decays. Many pond fish eat this algae.

Identifying Features:

  • Long, hair-like strands, sometimes clumped
  • Attached to structures like rocks or pipes
  • Bright green coloring
  • Forms floating mats and clumps

[Photo of filamentous algae waving in water]


Chara, sometimes called muskgrass or skunkweed, resembles underwater grasses or stems with branching thalli. The plant-like algae grow anchored to pond bottoms, submerged except for small reproductive structures. They have a gritty texture and sometimes emit a skunk-like odor.

Chara provides food for fish and helps filter sediment from water. But overgrowths can give water a foul taste and smell. Chara prefers alkaline water.

Identifying Features:

  • Submerged stems and structures resembling plants
  • Gritty or crusty texture
  • Gray-green to dark green coloring
  • Musky or skunk-like odor

[Photo of chara algae underwater]

Planktonic Algae

The planktonic algae category covers diverse microscopic algae suspended in pond water, including green algae. Planktonic algae form the base of pond food chains, serving as essential food sources for small aquatic organisms like zooplankton. Diatoms are perhaps the most important type of planktonic algae.

Too much planktonic algae may indicate an imbalance, but generally these algae are beneficial. A microscope is needed to examine them in detail.

Identifying Features:

  • Microscopic, can’t see individual algae
  • Float suspended in water column
  • Cause discoloration of water in blooms

[Photo of water sample with microscopic algae]

Blue-Green Algae

Cyanobacteria, commonly called blue-green algae, are potentially toxic bacteria that can form harmful algal blooms. Despite their name, they are not a true algae. Dense blue-green blooms look like thick paint or pea soup on the water’s surface.

Contact with blue-green algae irritates skin and is dangerous if ingested. The bacteria release toxins that deter grazers, leading to die-offs of fish and wildlife. Preventing blue-green algae is critical.

Identifying Features:

  • Blue-green coloration in water
  • Dense surface scum layer
  • Foul, decaying odor
  • May form streaks or dots

[Photo of blue-green algae bloom]


Diatoms are single-celled, encased algae that generate energy through photosynthesis. Their cell walls contain silica, allowing them to readily sink. Diatoms are a key food source in ponds, and also produce oxygen.

During diatom blooms, they turn water golden brown, which is beneficial. After population explosions, dead diatoms accumulate on the bottom into sediment. There are thousands of species.

Identifying Features:

  • Microscopic cells viewable under microscope
  • Golden-brown, sandy coloring in water
  • Settle on bottom after blooms
  • Important food source for animals

[Photo of diatoms under microscope]


Nitella are branched, slimy filamentous green algae that grow underwater attached to sediment, rocks and other surfaces. Their structures resemble aquatic plants with whorls of narrow branching leaves. Nitella provides habitat for small aquatic invertebrates.

Overgrowths can contribute to oxygen depletion as decaying material accumulates. Nitella prefers warmer water temperatures. It is not toxic.

Identifying Features:

  • Complex branching structures reminiscent of plants
  • Attached to pond bottom
  • Green, brownish or grayish coloring
  • Slippery texture

[Photo of nitella algae underwater]

Identifying Harmful Algae

Using this pictorial guide, you can start recognizing different types of pond algae based on visual characteristics and growth habits. Properly identifying algae allows you to take appropriate action to control overgrowth.

Learn to quickly identify potentially toxic blue-green algae by its thick surface blooms and blue-green color. Understanding which algae varieties are beneficial, like diatoms, lets you support the best pond habitat. With practice, you’ll be an algae identification expert in no time!

Green Algae (Chlorophyta)

Green algae is found in many different water types, including salt water and fresh water. Photosynthesis is the process by which green algae, which scientists call an “informal” group, turn sunlight into starch that can then be eaten.

All green algae has a high concentration of chlorophyll A and B. Both compounds are responsible for giving green algae its “green” color. This group of algae can be different shades of green depending on how much chlorophyll and other minerals and nutrients are in the water. In many lakes and ponds, green algae takes on the softer, more natural colors of the plants and animals around it.

This group of species can be planktonic or even microscopic, which makes them easy to spot during a big algae bloom. On the other hand, green algae can sometimes grow in large mats and clusters throughout the water column.

Brown Algae (Phaeophyta)

Brown algae contains fucoxanthin, a pigment not found in red or green algae groups. Phaeophyta is most commonly found in marine environments, and dominates rocky shorelines throughout much of the colder regions.

The majority of species found in the brown algae group are rooted in the ground. They tend to root down in environments of structure, usually characterized by rocks, shell beds, submerged logs, or even docks.

Brown algae in ponds can be a light beige or tan color, a yellow-brown color, or even black. Many of the giant kelp forests we picture bordering coastlines contain species of brown algae. Some of the most common species of brown algae include sargassum, turbinaria, and macrocystis pyrifera.

What are the types of algae in garden ponds | Any Pond Limited | UK


How to identify algae in a pond?

Planktonic algae is identified by causing the water to look green, brown or reddish and is sometimes confused with muddy water. Blooms can occur rapidly turning a clear lake or pond into a greenish color within a day or two.

What types of algae are there in ponds?

Of all types that can grow in a pond, euglena, blue-green, string, green water, and Chara algae are the most common. While most people assume that algae is bad for ponds—and an overgrowth can be harmful—it can be beneficial in the right amount, oxygenating water, feeding animals, and much more.

What does toxic algae in a pond look like?

ATTENTION: Cyanobacteria blooms/HABs can produce toxins that are harmful to humans and animals. Cyanobacteria get their name from their blue-green pigment but blooms can often look green, blue-green, green-brown, or red. Algae and aquatic plants are usually green but can appear yellow or brown as they die down.

How do I identify pond algae?

We also include pictures for easy pond algae identification. The algae you are most likely to see is the free-swimming type. The color of this algae may vary but the most common type is the one that causes your pond water to turn green. Known as planktonic algae, each individual alga is a single-celled organism.

How many types of algae are there in a pond?

From complex macro-algae like giant sea kelp to simple single-cell planktonic algae, there are more than 150,000 known types of algae . Luckily for pond owners, only a small fraction of these different types of algae grow in ponds!

Can algae grow in a pond?

Where there is water there will be algae. As a pond owner, it is important to be able to identify the different types of algae that can grow in your pond. When you can do this, you’ll be able to determine if the algae needs to be removed or if they are good for the ecosystem.

What is a pond algae?

In terms of appearance this form of pond algae is very recognizable. They are very small bodies, and contain chloroplasts which gives them their distinctive bright green color. They can provide a bountiful source of food and energy for smaller omnivorous fish who are near the bottom of the food chain.

Leave a Comment