WASHINGTON — Environmental groups are bracing for the Trump administration to approve controversial testing along the Eastern Seaboard that would mark a significant step toward offshore drilling in waters off the coast of Florida all the way north to the Delaware Bay.

Five geophysical survey companies are seeking federal permission to shoot pressurized air blasts into the ocean every 10 to 12 seconds around the clock for weeks and months at a time, seeking fossil fuel deposits beneath the Atlantic Ocean floor.

The testing, which would cover 330,000 square miles of ocean, faces fierce opposition from environmental groups and local officials because of the possible economic and environmental effects.

Because the underwater blasts are louder than a Saturn V rocket launch and can be heard by monitoring devices more than 2,500 miles away, scientists fear long-term exposure to the noise could cause hearing loss and impair breeding, feeding, foraging and communication activity among dolphins, endangered whales, other marine mammals and sea turtles.

Some worry that the blasts could cause mother whales and their calves to become separated. Commercial and recreational fisheries could also be affected if fish change their breeding and spawning habits to avoid the noise.

Others fear disoriented marine life could collide with the vessels that tug the air guns or become entangled in their lines. Oceana, an international conservation group, estimates that 138,000 marine mammals could be injured in the testing process.

Seventy-five marine scientists asked the Obama administration in 2015 to reject seismic air gun testing in the Atlantic because of these threats. Twenty-eight marine biologists did the same in 2016 over concerns that testing would harm the estimated 500 endangered North Atlantic right whales.

“That’s the species we are most concerned about,” said Doug Nowacek, associate professor of conservation technology at the Duke University Marine Laboratory in Beaufort, North Carolina. “They are in decline. They live coastally along the U.S. They were hunted (by whalers) and they were slowly recovering.”

These and other concerns are why the survey companies must first obtain Incidental Harassment Authorizations from the National Marine Fisheries Service and final approval from the Bureau of Ocean Energy Management before the testing can begin.

In a Jan. 23 letter to the National Marine Fisheries Service, trade groups representing the oil and gas and geophysical services industries said seismic testing is the “most effective, commercially available technology” to find oil and gas deposits.

The public comment period on the IHA applications ended in July, and most stakeholders say they think the geophysical survey companies’ authorizations are inevitable.

“They could reject them, but that is unlikely. It basically has never happened. Even under other administrations,” said Lara Levison, Oceana’s senior director for federal policy.

To better protect marine life, Oceana and groups such as the Marine Mammal Commission, the National Audubon Society and the Sierra Club want additional safeguards and restrictions on testing vessels.