BOSTON (CBS) — Some brown “gunk” has been spotted floating in Boston Harbor and it has residents worried that the city has returned to the “bad old days” when Boston Harbor was dirty.

“It sure is yucky,” said Bruce Berman of Save the Harbor, Save the Bay. He was talking about a brown substance that has appeared in the harbor.

“A number of calls that we got told us that they thought that cruise ships had discharged sewage on their way out of the harbor,” Berman said.

Another harbor visitor said she saw it on the way from Winthrop.

“I saw it in Winthrop and on the ferry on the way over and I have no idea of what it is,” she said.

“When it comes up on the shore, sometimes people mistake it for sewage,” Berman said.

Mistaking it for sewage is understandable, especially since the city used to dump raw sewage directly into the harbor.

The brown algae floating in the harbor. (Photo credit: WBZ-TV)

Berman says it’s not sewage. Instead, it’s a type of brown algae and it’s harmless.

“It’s a rather related seasonal bloom and it’s not uncommon. We just want people to know that they have nothing to worry about,” he said.

He adds that it’s not just in Boston Harbor. The brown algae has appeared along the coast.

“This extends from Nahant to Nantasket, and it probably extends to Cape Cod Bay,” Berman said.

Berman points out that the city and the harbor have made progress over the past thirty years.

“Thirty years ago Boston Harbor was the harbor of shame. We were a national disgrace,” he said. He credits the people of Massachusetts and the Massachusetts Water Resources Authority who have invested five billion dollars in cleanup efforts.

“It’s transformed the city and it’s given us back our beaches,” he said.

Berman expects the algae to be around for a few more days, but it’s still harmless.