There are numerous kinds of algae that form in a pond. They can be divided into two groups – suspended (tiny single-celled organisms responsible for green water), and filamentous (stringy strands such as blanket-weed and silkweed). Neither group is associated with an unhealthy pond, although green water and big mats of stringy green strands can be distressing to a pond owner. Algae are a beneficial plant, even if uninvited in the pond!
 
Suspended algae are usually most prevalent in a pond during spring, when the nutrient level is abundant, plants are still small, and the water is warming up. An algae bloom (green water) generally lasts until the submerged plants have proliferated, and the surface plants have multiplied enough to shade the surface of the pond (about 70% coverage). Plants use nutrients as fertilizer, and once plants are well established, the nutrient level is lowered, and the green water disappears.
 
Green water will disappear if allowed to run its course. A UVC will speed up the process. Whatever you do, resist the temptation to drain the pond. Fresh water is only a temporary fix as it is very high in minerals and will quickly turn green.
 
It is common to use biological products or chemicals to treat green water. Bear in mind that suspended algae consist of billions of single-celled plants that reproduce at an alarming rate. Repeated dosages are required.
 
Filamentous algae are usually found in otherwise clear pond water. Blanket-weed tends to form large floating, and partly submerged mats. It can be easily removed from the pond with a net or stiff brush. Silkweed is a dark green string algae, and tends to form in shallow water, anchoring itself to submerged plants, the stems of water lilies and rocks.
 
In sunlight, filamentous algae produce a lot of oxygen. The oxygen is trapped in little bubbles between the tangles of algae.
 
This type of algae reproduces by not only dropping spores to the bottom of the pond, but by single filaments touching each other.
 
Mild algaecides are available (Sera Pond Clear) to remove filamentous algae – any chemicals must be used according to directions, and with caution. The clumps of dead algae must be removed from the pond to prevent pollution and oxygen depletion. If available, add extra aeration to the pond water.
 
Cold temperatures do not kill algae - the cold merely drives algae into dormancy.
 

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Web Administrator - Isa Webb.
Last Updated: Wednesday February 24, 2010