Working with Nature

What are Algae?

Algae are the simplest forms of plant life. Much like any garden weeds they flourish in warm bright conditions. They are fed by nutrients provided by over rich soil used in the planting of aquatic plants and by nitrates in tap water and by the waste products of fish, or ducks, when they are present.

There are three main groups of algae:

Unicellular 'green water' algae - which can make the water look like pea soup, and of which the poisonous blue/green algae, seen as a bloom on the water, are members.

Cott or blanketweed

Filamentous algae - which form long filaments and floating mats of 'blanketweed'. Spirogyra, noted for its slimy outer coating, belongs in this category with others such as Cladophora and Vaucheria which can only be identified accurately with a microscope.

Stonewort

Stoneworts - which can be mistaken for plants but are a more highly developed form of algae and can be quite fragile to handle.

Spirogyra

Photos courtesy of the Centre for Aquatic Plant Management

Control of Algae

All forms can cause serious problems in ponds if not controlled. Algae produce large quantities of oxygen during the day but the decay of dying algae demand oxygen in considerable quantities resulting in severe oxygen depletion overnight. In conditions of heavy algal infestation aquatic plants become vulnerable to pests and diseases and fish become distressed.

Maintaining a good stock of oxygenating plants will provide competition for the nutrients and shade against the sun, they will also help to maintain healthy oxygen levels in the pond. However, where more than a few fish are to be kept, a pump and biological filter will be required to deal with their waste products.

It is generally easier to keep weeds under control than to eliminate them once they are well established. This is the case with algae and particularly with blanketweeds. Persistent strains are more easily brought under control in the cooler months when they are less active. Do not think that because they have died back in the winter that blanket weeds are dead. Their spores will be alive, just waiting for a little warmth and sunshine to bring them to full activity again. To prevent recurrence of algal problems, continuous treatment with Pond Pads should be maintained.