Green Algae, Thread Algae in Waters

Algae cover the ground, green algae float on the top.

What are algae?

Algae are low plant organisms, mostly living in water, which are organized as unicellular organisms or as multicellular organisms. The name “Alge” is a colloquial, non-organic name.

More than 3 billion years ago life began with the first green creatures, the archaebacteria and cyanobacteria. These are also called blue-green algae.

What do algae need to live?

Algae don’t need much to live on. Nutrients from the water such as phosphate and nitrate, but above all sufficient sunlight are sufficient for them.

How do algae originate?

Algae produce biomolecules from water and carbon dioxide. The green substance chlorophfeyll, which converts sunlight into energy (photosynthesis), is present in the cells of the algae. With the help of light, carbon dioxide (CO2) and nutrient salts (phosphate, nitrate, etc.) the cell substance of the alga grows and produces fats, proteins and sugar.

The alga is divided into different groups:

  • Prokaryotes – organisms without a cell nucleus. Prokaryotic algae are called cyanobacteria, blue-green algae or smear algae.
  • Eukaryotes or eukaryotes – Organisms with cell nucleus and cell membrane, approx. 10-100 times larger than prokaryotes.
  • Eukaryotic algae are all other algae: Green algae, brown algae, diatoms, euglenophyceae, dinoflagellates, chrysophyceae, haptophyceae, cryptophyceae, etc.

Green algae and thread algae

To the Grünalgen belong also the thread algae which in the pond with Nährstoffüberangebot and seichtem water gladly spread out, to the plague become.
Green algae and thread algae in garden ponds

Green algae also include thread algae, which form green algae mudflats and are very common in ponds. In the classical classification of algae, the chloromonadophyta, yellow-green algae, gold algae, diatoms and brown algae are counted as classes in the heterocontophyta group.

Filamentous algae are sometimes referred to as thread algae or pond foam. They appear like fine green threads that form floating carpets and are often moved across the pond by the wind. These algae are often found on rocks, flooded trees, other aquatic plants and jetties.

Macrophytic algae resemble real plants because they seem to have a stem and leaves and are rooted in the soil. A frequently occurring macrophytic alga is called chara or musk grass (because of its strong musk-like odour). Chara feels rough when touched due to lime deposits on its surface. This has brought her another often used name – stone root.

Algae problems

For the most part, algae are of little value for your garden pond or lake. The filamentous forms (thread algae) and the plankton have a gigantic reproduction rate and their sudden death can cause an oxygen deficiency. The oxygen needed for the fish in ponds and lakes can be provided by other aquatic plants in the pool that would thrive without competition from the algae.

Algae problems are usually caused by an excess of nutrients (nitrates and phosphates) in the pond. From the moment a pond is created, nutrients from the environment are washed into it. The older a pond gets, the more nutrients it has accumulated and the more susceptible it is to algae problems. The water derived from fertile fields, meadows and pastures, forage grounds, disinfection tanks and irrigation fields accelerates the accumulation and growth of algae in the pond.

Excessive algal growth will atrophy or suppress other forms of aquatic plants. In addition, the sunlight required for normal growth is blocked. Problems with the taste and smell of drinking water and sometimes even the death of fish are also associated with the excessive growth of plankton. Filamentous and macrophytic algae often form dense plants that make fishing, swimming and other recreational activities almost impossible. A complete coverage can prevent the penetration of sunlight and restrict the production of oxygen and the food components needed for good growth of fish stocks. If the presence of algae prevents the planned use of the pond, a method of controlling the algae should be considered.

Algae control

The algae explosion and carpets from thread algae can be removed with a rake, a cheese-maker or similar equipment. However, this method of algae control is very labour-intensive and offers only temporary control. In some cases, the algae seem to regrow just as quickly as they are removed.

Before using chemicals you should consider the possible contamination of household water supplies and waiting times for irrigation of livestock, fish consumption, swimming and possible skin irritations.

A “biological control” occurs when one life form is used to control another or to manipulate the biological balance in such a way that an unwanted plague is adversely affected. It is wise to be cautious when deciding on biological control. It can subsequently turn out to be unfavourable if the life form introduced becomes a greater problem than the original plague.

“Barley Straw” was tested in England by the Centre for Aquatic Plant Management for the possibility of controlling plankton and filament algae. These tests have been continued continuously over the last 15 years. “Barley Straw” and other straw species have been used in the United States occasionally with very mixed results and will not solve the problem. can be completely resolved.

Further algae information and tips

Fighting thread algae

The “thread algae” is not a botanical-systematic term, but a collective term for algae visible to the naked eye – tufts, balls, cotton tufts or mats. Thread algae grow and stick under water to aquatic plants, stones and dead wood.

Thread algae tufts, wads or mats as they appear typically in garden ponds

Thread algae in spring and summer

Thread algae develop very quickly in spring and early summer because they are the first nutrient consumers in water. By the time the aquatic plants grow, thread algae begin to grow at lower water temperatures. Due to this advantage, the thread algae grow almost explosively.

Thread algae are green algae

Thread algae have different manifestations. Mostly they appear as long thin threads (from a few centimeters up to several meters), which are partly interwoven in themselves. In many cases, the long-threaded green algae are interwoven in such a way that they can hardly be untangled.

Depending on the time of day, thread algae rise up and float as mats on the water surface. If they sink, they cover the bottom of the pond. Thread algae are adaptable and can become accustomed to chemical poisons, so that they become more and more resistant to them with the increasing use of chemical agents to combat them.

Thread algae develop when the water values are too high, i.e. the nutrient content in the water is too high. Usually a too high phosphate (phosphorus) value is the cause for the thread algae formation. With a lot of underwater plants you can contain thread algae after several years.

What to do against thread algae?

With high-precision click tones against thread algae: The click generator sends click sounds under water through the pond that are above the hearing frequency of humans and animals and are not audible. The vacuum in the middle of the algae cell, however, is resonated until it breaks and the algae dies.

Existing thread algae within seven weeks. By manually removing the algae during the transition phase, the phosphate in the water, one of the main nutrients of the algae, is removed.

How does the phosphate get into the garden pond?

Phosphate and other nutrients are contained in lawn fertilizer and nutrient-rich garden soil and are often washed into the pond by heavy rainfall. Also fish excrement and remainders of fish food as well as foliage promote algae growth.

Tips for combating thread algae

Thread algae have long Fäden
Thread algae have long strings & enough nutrients to grow up to several meters length !
  • When constructing the pond: ensure good shading and install very shallow areas.
  • When colonising the pond: use fast-growing aquatic plants, combination of pure underwater plants and marsh bed plants, use none or only very few fish, use thread algae repellents (such as Koi, Siamese trunk barbs) only in fish ponds.
  • When maintaining the pond: Do not fertilize pond water, minimize water exchange (no flow), cover the pond in autumn with a leaf fall net, place tannin-producing peat bags or sacks of rye straw in the water, fish thread algae by hand.
  • EM Effective microorganisms: Starter bacteria support pond cleaning, counteract turbidity, strong odours and algae growth. With controlled plant growth, zooplankton, which serves as food for numerous other aquatic organisms, can develop and thus create the basis for a stable and closed cycle. This is important for the development and preservation of the water. For optimal results, EM is combined with an algae eliminator.

Further information

Algae and Algae Species

There are thousands of algae species. In the classical classification of algae, the Chloromonadophyta, yellow-green algae, gold algae, diatoms and the brown algae are counted as classes to the group Heterokontophyta.

Green algae

Green algae types such as Chlorophyta, Chlamydomonas, Spirogyra, Cladophora, Hydrodictyon, Volvox, Spirogyra – spiral algae, Plantosphaeria, Sphaerocystis. The green algae also include the filamentous algae, which form green algae wadding. They often appear gelatinous.

Through the gas in the bubbles, the green algae drift to the surface and form a foamy carpet.

Blue-green algae

Blue algae (cyanobacteria) are not algae, strictly speaking, but bacteria, which at first glance have a similar appearance to algae and are commonly counted among them. With strong eutrophication, ie too high nutrient content, massive surface blooms or algal blooms form.

Blue algae in the lake form an oily film on the water surface.
Blue algae in the lake form an oily film on the water surface.

Brown algae

Brown algae (Phaeophyceae) look brownish and have a form of branched filaments in the garden pond. Brown algae are often found on plants and stones in fresh water

Brown algae like to accumulate on stones in shallow places from the pond.
Brown algae like to accumulate on stones in shallow places from the pond.

Brown algae in the saltwater look completely different, with large leaves and form up to 100m long threads, with which they root themselves in the soil. Brown algae in the sea can be found in cooler regions.


Diatoms (Bacillariophyta) are brown colored and called by a hard mineral shell, a cell envelope also Frustel. The brown alga consists mostly of silicon dioxide, as well as the brown alga. Silicon dioxide (SiO2) has the property of being very hard and is resistant to chemical agents.

Diatoms (250X) are a type of micro-algae. Over 100K different species exist. Foto: Kevin Dooley
Diatoms (250X) are a type of micro-algae. Over 100K different species exist. Foto: Kevin Dooley

More information about various types of algae:

Spirogyra algae cell under the microscope

These photos were taken with normal optical microscopy techniques under 400 magnification and show the effect of clicks on the algae cells:

The algae release creates acoustic clicks and emits click sounds under water. The hollow bodies, vacuole of the alga get into a squeeze through the high-precision clicks and tear. The cell juice comes out and the alga dies naturally.

Other species of algae under the microscope

Image source & friendly permission by NERC CEH

Additional Information