Dredging that the Navy says is needed to allow a $1 billion warship to safely transit the Kennebec River is under way, allowing the Navy to keep to its timetable for setting sail and commissioning the ship at a ceremony in Florida.

The Army Corps of Engineers began dredging this week after the state Board of Environmental Protection and a federal judge rejected efforts to stop the work. Critics said dredging at the height of summer could harm the endangered short-nosed sturgeon and other wildlife and jeopardize the livelihoods of clammers.

The Navy and Bath Iron Works contended that with sand and silt deposits in the river channel, the Spruance’s bulbous sonar housing could hit the river bottom as it traveled 13 miles downriver from Bath to the ocean.

The 510-foot-long ship is due to leave the shipyard in September for a commissioning ceremony Oct. 1 in Key West, Fla.

Shipyard spokesman Jim DeMartini said the Navy took the lead on the dredging project since it already has taken ownership of the Spruance. But it’s important for the shipyard and its 5,300 employees to know they can stick to the timetables.

“With fewer ships being built by the Navy and more intense competition taking place for those that are being built, BIW and its customers need to be certain we can safely navigate Bath-built ships down the Kennebec River as we have for over 125 years,” DeMartini said Friday.

Dredging is usually done in the winter, but the Army Corps sought emergency approval to remove 70,000 cubic yards of sand and silt in the summer to ensure that the Spruance is delivered to the Navy on schedule.

Steven Hinchman, an environmental lawyer who opposed the project, said the Army Corps shouldn’t be dredging during what’s the most biologically productive time of the year. He also said the amount of material that’s being dredged is far greater than what’s necessary to ensure the ship’s safe passage.

“Our claim all along has been this is excessive,” Hinchman said Friday. “You can get the ship out safely without an excessive dredge.”

The Spruance can sail safely to the ocean at high tide with a small buffer as long as the river’s navigation channel is maintained at 27 feet deep.

Soundings in the river last winter indicated that silt and sand had reduced the channel’s depth to less than 20 feet just south of BIW and less than 27 feet farther downstream toward Popham Beach, creating a “substantial risk of grounding,” the Navy said.

Delaying the ship’s commissioning would send ripples throughout the Navy, which is strained because of demands around the world and the fact that the Navy is 28 ships shy of its stated goal of having 313 ships in operation, wrote Vice Adm. Richard Hunt, commander of naval surface forces, in a court filing.