This is pretty interesting and something that should be considered for the benefit of the environment and the existing marine life providing it doesn't harm cause any damage/harm during the decomissioning process and any clean-up.
"Off the coast of Southern California, there's an underwater city. A thicket of almost 30 enormous steel oil rigs, each as large as a skyscraper, bolted to the floor of the ocean. Most of them are elderly, aging giants—and soon, the state will need to make a decision about whether to rip them up or let them stand. Either option comes with huge risks."
"But over the next few years, every last one of these rigs will go dry or be decommissioned. Until 2010, state law required that they be removed entirely—but it now allows the option to convert the rigs into artificial reefs instead."
As many scientists have pointed out, these decades-old structures play host to incredible amounts of sea life. In the Gulf, part of an increasingly popular solution called "rigs to reefs," decommissioned oil rigs are sliced off at the water line to preserve the ecosystems—essentially creating artificial reefs below the surface."