Hardly anyone who’s visited the Baltimore harbor in recent weeks has come away feeling that the urban waterway is well.

The signs of sickness have been impossible to miss.

Thousands of dead Atlantic menhaden bobbed on the surface in late September — the harbor’s third major fish kill in barely a month. For close to three weeks since, the water has taken on a milky green hue and oozed a smell reminiscent of a heavily used porta-potty.

“Suffice to say that if the Baltimore harbor were a patient, that patient just had a heart attack,” said Adam Lindquist, vice president of Waterfront Partnership of Baltimore, on Friday.

Harbor advocates like Lindquist say the greenish color that’s overwhelmed the harbor in recent weeks — known locally as a “pistachio tide” — is the longest event of its kind they can recall. Its stench has wafted over the waterfront and reached Canton, Johns Hopkins Hospital and, another downtown booster said Friday, even miles away into Northeast Baltimore.

But speaking Friday in the Fells Point offices of Brown Advisory overlooking the teal-green water, Lindquist and other harbor advocates expressed confidence that the harbor is getting better — despite its sickly look and smell. The latest assessment of the harbor’s health by Waterfront Partnership suggests that the water’s safety for human recreation is steadily improving.

The nonprofit Waterfront Partnership, which has led a campaign for 15 years to make the harbor swimmable, isn’t deterred by recent challenges. Lindquist told attendees Friday that the group is looking into installing the harbor’s first permanent swimming area.

The pistachio tide is harmless to humans, and when it comes to safety for swimming, Waterfront Partnership gives much of the harbor a passing grade in its 2025 Healthy Harbor Report Card. Pockets like the Inner Harbor, the Downtown Sailing Center and Canton Waterfront Park received C or C+ grades, meaning water samples passed state swim safety standards in more than 70% of tests.

The Jones Falls and Patapsco River outfalls were less encouraging: Those areas earned a D- and an F, respectively.

But Fells Point, where Waterfront Partnership has hosted organized swim events in recent years, notched a B. When the partnership first graded harbor health in 2011, this area failed to clear state recreation standards a single time. In the latest assessment, it passed in 84% of cases.

Even there, though, the harbor’s volatility foiled plans for the partnership’s organized swim this summer. Two attempts to hold the event were rained out after storms flushed sewage and runoff into the harbor.

Lindquist said Waterfront Partnership hopes to hold “pop-up” swims next year, events announced days rather than months in advance to work around the weather.

These pistachio tides are to some extent seasonal events, experts said. The drop in temperatures with the start of fall has caused waters to turn over, bringing up an oxygen-deprived layer from the bottom. With it, sulfur bacteria rose to the top, multiplying in the sunlight, sucking up oxygen and turning the harbor green and smelly.

But while “normal-ish,” as Eric Schott, an associate professor at the University of Maryland’s Institute of Marine and Environmental Technology, put it Friday, advocates worry about how long this pistachio tide has lasted.

Why it’s happening — especially on the heels of other positive trends for the harbor — remains a mystery to scientists like Schott. He outlined plans Friday for the partnership, researchers, developers and city leaders to study the question and potential solutions over the next year.

Some harbor advocates emphasize how far the harbor has to go still.

Blue Water Baltimore released its own assessment of the harbor’s health earlier this year that offered a more dour conclusion: Despite major investments to curb pollution, water quality measures in the harbor and its watershed actually declined somewhat in the last decade.

“If anything, the last few weeks have proven how important the Inner Harbor is, and how delicate an ecosystem it is,” said Alice Volpitta, Baltimore Harbor Waterkeeper for Blue Water Baltimore.

Waterfront Partnership gave the ecosystem — distinct from its health for human swimming — an overall C grade in its new assessment, same as last year.

For now, the system is “flatlining,” Lindquist said.

The pistachio tide has depleted oxygen across the harbor almost completely. Just about all of the fish, crabs and eels that swam there this summer have either died or fled.

It’ll take a big event, maybe a significant rain, to restore the ecosystem, Lindquist expects.

It needs the “ecological equivalent of a defibrillator,” he said: a massive pulse of oxygen so life can return.