The U.S. Coast Guard is investigating an oil slick spotted in parts of the Inner Harbor on Wednesday afternoon, a common problem advocates attempting to clean up the city’s waterways must confront after rainstorms.

City agencies were also part of the initial response on Pier 5, where a gray sheen could be seen in the water early in the afternoon.

The Maryland Department of the Environment is also investigating.

“Our emergency team estimated about three to five gallons of fuel oil in the water,” said agency spokesperson Jay Apperson. “We provided sorbents for oil recovery. It appeared to have come through the Jones Falls from an undetermined source upstream. We observed no additional fuel discharging from the Jones Falls outfall to the Harbor.”

Adam Lindquist, vice president of environmental programs for the Waterfront Partnership of Baltimore, said oil from the water is getting picked up by Mr. Trash Wheel, the organization’s googly-eyed semi-autonomous trash interceptor at the mouth of the Jones Falls. He added that the state environment department also sent sweeps to help collect the oil.

Earlier in the day, the slick wrapped around several piers, hugging the borders of the Pier 5 Hotel Baltimore and the National Aquarium. By 2:45 p.m., the sheen had dissipated near Pier 5.

Alice Volpitta, the Baltimore Harbor Waterkeeper with the advocacy group Blue Water Baltimore, said the slick was likely caused by polluted storm water runoff. Lindquist added that when it rains, it’s very common to find oil slicks, and even oil spills, in the water.

Volpitta said Blue Water Baltimore and its partners report pollution incidents to the Coast Guard’s National Response Center about every other month, including this most recent one. Typically, after every report, the Coast Guard dispatches investigators to the scene, Volpitta said.

For this oil slick, she added, since the Coast Guard could not link a continuous discharge of oil to a specific source, there is nothing to do but wait for the oil to dissipate.

“It’s kind of an unfulfilling outcome because folks see something that’s clearly not right,” Volpitta said. “They know to report it, but there’s not a really good resolution at the end of the day.”

The crux of the issue, according to both Lindquist and Volpitta, is Baltimore City’s storm drainage system.

“A lot of people think storm drains get filtered or go to a plant somewhere,” Lindquist said. “That’s actually true in some cities, but in Baltimore, it is not true. Our storms drains go right into our streams and the harbor.”

But, until those improvements are made, the harbor is relying heavily on Mr. Trash Wheel and the other members of the trash wheel family to help clean the water of trash and oil, Lindquist said.

And, at least for the next couple of days, this oil slick will have Mr. Trash Wheel hard at work, Lindquist said.

brenna.smith@thebaltimorebanner.com