Brittany’s ‘Green Tides’ – a future threat to the Solent?

The eutrophication of coastal waters has led to disturbing phenomenon of ‘green tides’ across the Channel in Brittany. We are all now aware of the nitrate pollution in our rivers, estuaries and inland seas and the resulting build-up of green algae. What we in the UK are less aware of is that decomposing green algae emits hydrogen sulphide, fumes which can potentially be life-threatening.

Image credit – Marie Le Gac

Parts of the French Brittany coast have become ‘no go’ areas, covered with a layer of algae from the family Ulvaceae, commonly known as “Sea Lettuce”, around which the air is thick with the smell of rotten eggs. The algae, which in places can be up to 1 metre deep, forms a hard crust which, once broken, gives off this lethal toxin. Blame is clearly being directed at intensive arable farming with its use of nitrate fertilisers, together with the waste generated by pig, poultry and dairy farming. But what can be done? Seemingly, beach clearance is the only answer but this too has its hazards.

This type of pollution is not limited to France as similar reports have been received from the United States and Mexico. Toxicologists have studied the chemical composition of the decomposing algae and the results are alarming. France has reported four deaths as a direct result of exposure to the hydrogen sulphide, including that of a lorry driver employed to remove the waste from the beaches. Much local wildlife has already suffered including many wild boar and France has cleared 5,000 tons of the algae since June 2021. The damage done to the local tourist industry has been significant.

Does climate change exacerbate the problem? French sources suggest that it does and as the French say, ‘the algae will become turbocharged’. Clearly the use of nitrates in fertilisers must be stopped though even if this could be achieved it would still take many years to eradicate the effect of the pollution. The French environmental community are fighting back, ‘Halte aux marees vertes – Halt the green tides’ – with demonstrations concentrating on the 114 sites around the Brittany Coast. A book, ‘Green Algae, the untold story’, has been published in French but to date, little has been done by the French government to reduce the cause of the pollution.

Here in the Solent, we do not yet see the same extent of algae growth but we must remain mindful that the current relentless growth in housing development and intensive farming will have serious consequences. Monitoring our rivers and estuaries is essential and we should each press our parliamentary representatives to ensure reduction in the use of nitrate fertilisers, reduction in waste from poultry and pig farms and the recycling of cattle waste as non-toxic fertiliser. Without the attention of politicians and the general public, the dangers experienced in France will inevitably occur around the Solent coastline.