From shore or diving at the reef are always mixed with the underwater beauty, plastic bags, cans, pieces of wood, batteries, lighters, plastic bottles…
So, what to do? Collapse all? No.
Often the waste has become a substrate for animals and, in some cases, removing it would cause new impact. If the object is already taken by sponges and corals, it is best to leave it there, unless it is a potential emitter of polluting chemical (batteries, etc.).
In short, you should remove everything that is derived from metal, plastic or rubber, are colonized or not, because the long term, bring about considerable losses.
Cans, plastic bottles and cups can not be regarded as artificial reefs are not fixed and even if they do not decompose completely, usually wander from one side to the other, polluting the sea.
So on your next dive, the hint is, why not bring your bag to collect and lend a hand to nature?