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How can algae be controlled?

Algae can cause problems when they form blooms in streams/rivers or in lakes/ponds. The problems may relate to aesthetics, tastes, odours, smothering streambed habitats, oxygen depletion (algae consume oxygen at night) or toxicity. If algal blooms are a significant problem, expert help is often required to choose the best solutions.

In some cases an option is to do nothing – just wait for nature to do the job, either by flushing during floods, or by the gradual increase in populations of algae-eaters such as snails in streams/rivers, or zooplankton in lakes/ponds.

Planktonic algal communities in lakes, ponds and wetlands will vary in composition between sites and between sampling dates. However, if you find you find planktonic algal communities with high abundances of taxa commonly found in sewage treatment ponds then you could reasonably assume the habitat is nutrient enriched. If algae are causing problems at such sites, then management activities designed to reduce nutrient inputs may be appropriate. Starving algae of nutrients may require an investigation into which is the limiting nutrient (reducing levels of that particular nutrient are most likely to reduce algal growth). The primary source of the limiting nutrient needs to be identified – is it nutrient loss from surrounding land, or is it wastewater discharges entering the system?

Algal growth can be limited by shading, so a long term solution for many streams might be to increase shade levels through planting suitable riparian vegetation. Lakes and ponds may be too wide for riparian vegetation to have any significant shading benefit, so nutrient limitation might be a better long tern solution. However, large lakes can contain large amounts of nutrients in their sediments, and it may take many years for these nutrient supplies to be reduced to the point that planktonic algae become nutrient limited. Ponds may be small enough that they can be more easily flushed by stream flows, or even temporarily drained. One method that has been used in many ponds with planktonic algae problems is the placement of barley straw in the pond. The barley straw releases chemicals that suppress algae growth.

Algal biomass can become excessively high in streams/rivers regulated by dams because these dams reduce the occurrence of scouring flows downstream, so a potential solution is to allow periodic releases of sufficient water to scour the downstream habitats.