On Tuesday night, BP said that the “active cleanup” of the Gulf of Mexico oil spill had been brought “to a close.” Later Tuesday night, the Coast Guard said the response to the spill isn’t over yet, “not by a long shot.”

The dueling news releases came out just before the fourth anniversary of the April 20, 2010, blowout on BP’s Macondo well. The Deepwater Horizon drilling rig caught fire and sank, 11 workers were killed and more than 4 million barrels of crude spilled into the gulf.

BP, which has vowed to “make things right,” said it issued its press release because the Coast Guard ended “patrols and operations” along the final three miles of Louisiana shoreline, capping a four-year effort that BP said cost more than $14 billion.

From now on, the Coast Guard and BP will not be scouring the coast for oil, but rather responding to specific reports of oil washing ashore.

BP said it wanted to note the “milestone” and said nearly 4,400 miles had been surveyed, with teams detecting oiling on 1,104 miles and doing at least some cleanup on 778 miles.

But Coast Guard Capt. Thomas Sparks, the federal on-scene coordinator of the Deepwater Horizon response, sought to stress that the switch to what he called a “middle response” process “does not end cleanup operations.”

“Our response posture has evolved to target re-oiling events on coastline segments that were previously cleaned,” said Sparks. “But let me be absolutely clear: This response is not over — not by a long shot.”

BP has been trying to bring the oil spill episode to a close and circumscribe costs that so far have reached $27 billion. Litigation over economic damages and federal fines under the Clean Water Act continues in New Orleans. The company has set aside roughly $42 billion for total costs.

At its April 10 annual meeting, BP chief executive Bob Dudley said: “We have looked to do the right thing by those who were affected by the accident and spill. But also to do the right thing by our investors when it became clear that the system for compensating claimants was subject to a considerable number of unfounded claims.”

Environmental groups criticized BP’s announcement. “It’s clearly premature to end the active cleanup,” said Raleigh Hoke, a spokesman for the Gulf Restoration Network, a nonprofit environmental group. “When oil washes up on shore, BP is no longer automatically obliged to go out there and clean up the mess. Now the onus is on the public, and state and federal governments to find the oil and then call BP in.”

Some experts said the switch is understandable.

“Of course, there is still some oil from the Deepwater Horizon incident left, particularly in coastal marsh areas,” said Edward B. Overton, professor emeritus of environmental sciences at Louisiana State University, adding that storms churn up the residue.

“I think oil residues will be around in small areas of the marsh for many years, but we can’t get rid of oil in marshes because the cleanup process will destroy more marsh and do more damage than is being done by the oil,” he said in an e-mail. He added that “this is why we don’t want oil to come ashore on coastal marshes, and use dispersants well offshore to keep the oil, to the extent possible, out of the marshes.”

BP spokesman Geoff Morrell said that “we have never suggested the work of the U.S. Coast Guard or BP is over. Our announcement yesterday merely highlighted the end of active cleanup of the gulf shoreline. We believe that is a very significant achievement.”

Overton said active cleanup efforts had probably “come to a point of diminishing returns.”

“It’s very analogous to having a serious illness that requires hospitalization,” he said. “At some point in recovery, the patient is sent home, but this does not mean the patient has completely recovered. And neither has our coastal environment, but we are much better off than we were in 2010,” immediately after the accident.