Z-Guard says ALWC has been seen to occur just below the water level or at low water level in tidal areas, although it has been said to be reported down to the seabed. On some steel piles it has been reported that up to 4mm per side, per year, have been lost due to the phenomenon.

The presence of these colonies of sulphur reducing bacteria are recognised by a soft orange coloured deposit, under which is a layer of black slime (iron sulphide). The reaction is characterised by a "rotten eggs" smell with the formation of hydrogen sulphide gas.

Just as it is causing a problem for steel piles in some ports and marinas, mooring chain can also suffer, says Glenn English, managing director of Z-Guard Zinc Anodes.

He says one 15kg zinc anode (seawater) or 5Kg aluminium anode (brackish water) can effectively protect up to 3m of chain against corrosion and ALWC for up to 5-6 seasons.

Z-Guard Zinc Anodes produce two sizes in mooring anodes;

one for 1/4" chain and one for 1/2".

Both are available in zinc and aluminium and are priced at £55.00 and £65.00 respectively, including VAT and carriage.

Glenn English at Z-Guard T: 0870 2421973 E: sales@z-guard.co.uk W: zguard.co.uk