Slimewatch UK: 8inch-thick carpet of algae is clogging South Coast




A vast slick of seaweed is choking the South Coast - threatening wildlife and playing havoc with boats, according to the Environment Agency.

The hot June and washout July created perfect conditions for the floating algae which has grown up to 8in thick in some harbours and estuaries.

Algal blooms are also hitting beaches along the French coast, where rotting seaweed above the high tide mark has released a potentially deadly toxic gas.

Clogged: The algal bloom on the shore of Langstone harbour in Hampshire



While the huge mats of weed on the coastline of Sussex, Hampshire and the Isle of Wight are unlikely to harm people, they pose a serious threat to plants and animals.

One of the worst affected areas is Langstone harbour, between Chichester and Portsmouth.

Locals describe it as one of the worst blooms since the algae began building up back in the 1960s. This summer, the thick slime covers an estimated 926 acres of British harbour.

Other areas badly hit include harbours at Portsmouth, Chichester, and Poole, the Hamble estuary near Southampton and the Medina estuary on the Isle of Wight.

The weed thrives on nutrients released from sewage works and the nitrate-rich fertilisers washed off farmland during heavy rain.

Hundreds of acres of mudflats along estuaries and harbours have now been taken over including Langstone Harbour, Portsmouth (above)

The unnatural level of algae growth is caused by nutrients released by farmland fertilisers and sewerage which cause the seaweed to thrive

The Environment Agency said it is unlikely to be dangerous to humans. Twice-daily tides mean the algae does not have time to dry out and bake - and so does not release toxic gas.

However, when it decays in winter it releases hydrogen sulphide into the water, killing marine life.

As it grows during the summer, the algae uses up vital oxygen in the water, killing shrimp, eel grasses and worms and depleting food for other wildlife such as fish and birds.

Walkers are being advised to avoid badly-affected areas as a precaution if they smell an odour of rotting eggs, since this would indicate poisonous gas is being released from the weed.

Picturesque: The harbour just two months ago before it was taken over by the algae



The Agency's marine expert Dave Lowthion said: 'We haven't been measuring the seaweed from year to year so we can't say how much the amount has gone up, but we had a fairly hot and sunny April and May which is when the stuff starts growing, and we've not had the storms needed to wash the weed away.

'The river flows are high after the wet July so nutrients are likely to have been entering the harbour.' Two species of floating seaweed are clogging up the South Coast - the spaghetti-like enteromorpha and sea lettuce, which has rufflelike fronds.

The Agency is taking samples of the weed and is using aerial mapping to see how it is spreading.

It said water quality is improving in the Solent - thanks to millions of pounds spent improving sewage treatment - and it expects weed levels to decline in the future.