Twenty whales believed to be part of a pod found stranded in the Everglades this week were spotted Friday afternoon moving closer toward shore, a sign they may be reversing their earlier, positive course, wildlife officials said.

The whales were about five nautical miles from the coast, one mile closer than Thursday.

“I am definitely concerned to hear about their behavior, that they are less organized, that they seem to be swimming very slowly,” National Oceanic and Atmospheric Administration stranding coordinator Blair Mase said. “They may have gotten to the point where they are exhausted.”

Earlier Friday, officials had been hopeful the whales were headed back to the deeper, colder waters that form their natural habitat about 20 miles out to sea. On Thursday, a Coast Guard helicopter spotted three pods of about 35 whales that had moved six miles offshore and into water about 18 feet deep.

“They could dive, they were swimming, and they had a straight shot to their home range,” Mase said of the short-finned pilot whales. “And they didn’t take it.”

Mase said the whales’ apparent movement inshore raises concerns something may be preventing them from going farther out to sea, such as an illness.

Eleven of the 51 whales spotted by a fishing guide Tuesday have died. Six were found dead Wednesday morning, and four were euthanized. One died Thursday.

Necropsies did not reveal any significant initial findings, though they did have empty stomachs, indicating their health may have been compromised. Scientists were awaiting the results of pathology tests to see whether there was any evidence of disease. According to NOAA, pilot whales have been known to carry the morbillivirus, which can cause skin lesions, pneumonia, brain and other infections.

A Coast Guard flyover Friday morning spotted only seven whales swimming in 12 to 14 feet of water. Two others that appeared to be closer to shore turned out to be dolphins, Mase said.

The larger group of whales could not be located.

But by Friday afternoon, Mase said the seven whales had joined a larger group of 20 heading south and inshore, in about 10 to 12 feet of water. There is no land in the immediate vicinity for them to beach themselves, she said.

From the start, NOAA and National Park Service officials have said the short-finned pilot whales faced significant hurdles. To get to deeper waters they faced a series of sandbanks, tributaries and patches of shallow water that Mase said were “almost like a maze.”

Wildlife volunteers were surprised when they arrived at the stranding site Thursday and found the whales had managed to move six miles offshore on their own.

“Quite the surprise,” Donna Buckley, a National Park Service volunteer said.

Donna and John Buckley had been the first to respond after the whales were found Tuesday afternoon. A call came across the parks radio, and the Buckleys were the closest volunteers to the remote western edge of the Everglades park.

When they got to the beach, John Buckley waded through the shallow waters in a canoe while his wife stayed aboard the boat, counting the whales drifting before her. In their 28 years as volunteers in the Everglades, they had seen only one whale stranded before.

The whales they were able to help save seemed ill, Donna Buckley said.

“They seemed very disoriented, confused,” she said. “They didn’t know which end was up.”