Define the Marine Growth - Underwater inspection of bridges?

Bridges on many inland waterways are relatively clean and free of marine growth. However, there is likelihood of marine growth and incrustations on underwater structures especially in marine/coastal areas. The marine growth can be seaweeds, barnacles and various types of bacteria and other simple organisms. From an engineering point of view, there are two main categories of fouling - soft fouling and hard fouling. Soft fouling is caused by those organisms, which have a density approximately the same as seawater.

They are easy to remove to facilitate inspection. Organisms causing hard fouling are much denser and more firmly attached to the structure and are, therefore, difficult to remove. Cleaning marine growth from the underwater portion of the bridge is almost always necessary during an underwater inspection. The extent of cleaning depends on the amount of growth present and the type and level of inspection.