The flow of oil from shallower parts of the Gulf of Mexico has slowed to a trickle over the years as production shifted to deeper waters, but much of the now-outdated equipment remains — rusting — in place.

“The depletion of shallow water oil and gas resources has left a legacy of active but quite old infrastructure still producing marginal but declining resources,” Donald Boesch, president emeritus of the University of Maryland’s Center for Environmental Science, testified Thursday.

He and other experts appeared before a hearing of the House Natural Resources Subcommittee on Energy and Mineral Resources as it examines the risks posed by aging and abandoned offshore fossil fuel infrastructure. Witnesses highlighted how pipelines left to deteriorate on the seafloor and leaky, abandoned wells pose environmental risks, in the form of both spills and contributions to climate change.

Many of the facilities that need to be retired are no longer operated by original leaseholders but have been passed off to smaller companies with less capacity to handle that process, posing substantial challenges to reliably sealing and decommissioning them.

More than 55,000 oil and gas wells have been drilled in federal waters, 97 percent of them in the Gulf of Mexico, and 59 percent of those wells have been either permanently or temporarily abandoned, Boesch said.

Thursday’s hearing came in the wake of a pipeline rupture off the coast of Southern California that has provided fresh impetus to environmental advocates and many Democratic lawmakers pushing to tighten federal oversight of offshore oil and gas operations. They cite a Government Accountability Office report earlier this year that found the Bureau of Safety and Environmental Enforcement has a number of blind spots when it comes to monitoring and decommissioning offshore oil pipelines in particular.

Rep. Alan Lowenthal, D-Calif., the subcommittee’s chairman, highlighted the impact of the recent California spill.

“It’s critical that we don’t simply move on and wait for the next accident to occur,” Lowenthal said. “Offshore oil and gas infrastructure, both in the Gulf and in the Pacific, is a ticking time bomb.”

Democrats have various proposals aimed at holding companies accountable for cleaning up their operations in the event of accidental spills or abandonment. They worry about companies dumping old infrastructure on shell companies that are then allowed to go bankrupt.

With that in mind, House Natural Resources Democrats included new fees on offshore oil and gas pipelines in their portion of the budget reconciliation package.

Republicans characterized the rhetoric from Democrats as overblown and part of a broader attempt to curtail the U.S. oil and gas industry, which they said would simply move production to places overseas such as Russia.

Rep. Pete Stauber of Minnesota, the top Republican on the subcommittee, said lawmakers on his side of the aisle believe in protecting the environment and supporting both safety requirements and federal conservation efforts funded by offshore oil and gas revenue.

“However, we draw a hard line on vilifying an entire industry that employs hardworking Americans earning high-quality wages and lets you and I put affordable gasoline in our vehicles,” Stauber said.

Republicans also pointed to the role oil and gas equipment can play in providing habitat to fish, as illustrated by one of the hearing witnesses, Greg Stunz, professor of marine biology at the Harte Research Institute for Gulf of Mexico Studies at Texas A&M University, Corpus Christi.

Stunz described how turning oil rigs into human-made reefs can be an effective way to increase fish populations.

“They produce reduced fishing pressure on natural areas; they’re an excellent example of a partnership between oil and gas industry and resource managers, where both the Gulf environment, in this case, economy and public can benefit,” Stunz said.

Democrats have acknowledged it’s appropriate to consider the impacts of removing equipment on fish habitats but made clear they will continue pressing for more regulation in the area.

Rep. Jared Huffman, D-Calif., pointed to two offshore pipeline safety bills that the full committee advanced Wednesday. He said they were far from transformative but still prompted strong Republican criticism.

“They were baby steps, and yet it sounded like the sky was falling,” Huffman said. “Every little thing we do to ask more of the oil and gas industry to make them clean up their mess means that we’re going to be supporting Putin and foreign competitors and we’re going to be ending the world order as we know it.”