When we first move to Knutsford in 1986 there was no generally recognised problem of blue green algae or cyanobacteria. There was a small sandy beach by the lake in Tatton Park, where people would go to picnic and bathe in the lakewater. Dogs swam in the lake without problem; even daughter’s Westie put his toes in.
Then, in the early nineties, notices began to appear about blooms of blue green algae in the water; dogs should not go in and people should definitely not bathe. They appeared with increasing frequency, and are now a permanent feature. The sandy beach is long gone.
Almost everywhere you go in Britain these algae seem to have got a hold, with a detrimental effect on other wildlife. Last year we witnessed dead Canada geese being removed from Shakerley Mere because of poisoning, suspected to be the very evident blue green algae.
Close up the resulting scum can appear ugly, but can sometimes give almost beautiful effects, as in the following picture.
So what causes these algal blooms and what changed?
According to the Centre for Earth and Environmental Science, Indiana University the combination of factors that trigger and sustain an algal bloom is not well understood, but these are the main factors:
- Nutrients – over-enrichment due to mainly phosphorus and nitrogen, arising from runoff from fertilised agricultural areas, lawns, land clearance, and sewage
- Temperature – Water temperatures above 25°C. Thus in temperate regions such as UK, blue–green algal blooms generally do not persist through the winter months
- Light – blue–green algae populations are diminished when exposed to long periods of high light intensity but have optimal growth when intermittently exposed to high light intensities.
- Stable Water Conditions – with low flows, long retention times, light winds, minimal turbulence. Drought, water extraction, weirs and dams all contribute to to this.
- Turbidity caused by suspended particles following rain.
If I might suggest a quick summary, modern industrial farming, badly managed waste water, global warming and over-exploitation of our rivers are the prime reasons.
As pointed out by George Monbiot, Britain’s rivers are dying due to similar factors.
There’s no quick fix. Moving to organic farming to maintain soil fertility is a no-brainer. As is reducing carbon emissions. This needs political change.