Any artificial reef - even a bad one - will act as a fish aggregating device, but only the good ones improve upon nature by creating something nature hasn’t provided.

In BC [British Columbia] waters, nature has already filled the bill nicely. Artificial reefs made of old ships and other cast-off materials are therefore unnecessary - and may even harm the environment by replacing existing natural habitats with less effective artificial ones. At the very least, we are altering marine habitat by sinking ships - somewhat akin to gathering a bunch of old wreck cars in the midst of a forest or grassland. This would create habitat for certain species (eg. rats), but would definitely alter the natural ecology.