Accelerated Low Water Corrosion (ALWC) can affect unprotected marine steelwork within the lower portion of the tidal zone. It is an aggressive form of microbially induced corrosion. ALWC is a result of the symbiotic relationship between two bacteria. Sulfate-reducing bacteria and sulfate-oxidising bacteria work together to attack unprotected steel. Corrosion rates have been commonly recorded at 0.5mm to 1mm per year, but may be as high as 4mm per annum.
ALWC is indicated by the presence of a bright orange sludge on steelwork within the low water zone. Upon removing the sludge, bare pitted metal is evident. The sludge will give off a metallic odour. ALWC can be prevented via the application of coatings, or cathodic protection.