Algal blooms in lakes
Algal blooms. The algae that commonly grow in lakes are a free-floating form (phytoplankton). Some species are cyanobacteria that have the potential to grow rapidly to form a high density of cells (bloom) and produce cyanotoxins.
In Canterbury, Lake Forsyth/Te Roto O Wairewa forms a bloom of the cyanobacteria Nodularia in most summers. This alga produces the toxin Nodularin, which has been known to kill stock and dogs that are in contact with lake water during a bloom.
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Algal blooms in lakes or still waters are commonly blue-green in colouration, but can also be red or yellow. They typically form thick scums on the surface, and may also develop foams at the water's edge.
What causes cyanobacteria algal blooms?
Warning sign.
The presence of extensive mats of cyanobacteria is linked with environmental conditions conducive to their growth. Favourable conditions include the right combination of warm temperatures, sunlight, low or stable river flows, and nutrients. The occurrence of mats or algal blooms is a natural phenomenon, but human activities, such as taking water from rivers or adding nutrients to waterways, can make things worse.
Are cyanobacteria always toxic?
No. There are several species of cyanobacteria, that may or may not be toxic, depending upon prevailing environmental conditions. However, if potentially toxic cyanobacteria are present in large numbers,
you should presume that the water may be unsafe for contact recreation or consumption.
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Some algae have toxins in their cells, and can be harmful if they are consumed.
Such algae present a risk to dogs which may eat algal mats, or ingest algae when they drink water from a watercourse. Other cyanobacteria may release toxins into the water surrounding them, which can affect those that contact or drink the water.
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