The movement to swim in the Baltimore Harbor is in full swing.

More than 150 people plunged in a year ago to demonstrate the water’s safety. Two days later, a woman swam 24 miles from the Chesapeake Bay Bridge to the Inner Harbor and enjoyed it so much she’s trying it again.

Despite recent optimism, though, testing suggests the harbor isn’t clearing up as many have hoped.

A new report card released Tuesday by the environmental nonprofit Blue Water Baltimore shows water quality measures in the Harbor and its watershed have declined somewhat since 2013, despite major investments to curb pollution.

Blue Water measures ecosystem health at 51 stations around Baltimore’s waterfront and streams and gave the Harbor a score of 49% for 2024 — a middling grade down slightly from the year before.

Alice Volpitta, the Baltimore Harbor Waterkeeper for Blue Water Baltimore, said water quality has languished despite huge investments in stormwater infrastructure and the region’s sewage system. She suspects that spending has been counteracted by familiar foes like development, persistent sewage overflows and climate change.

It can feel like the “Red Queen’s race” in Lewis Carroll‘s “Through the Looking Glass,” Volpitta said, in which the character Alice runs harder and harder but remains stuck in the same place.

“We are moving really quickly,” said Voplitta. “But the earth beneath our feet is moving faster.”

Even so, there are success stories within the harbor watershed. Concentrations of dissolved oxygen, necessary for underwater life like crabs and fish, scored 93% in Blue Water’s testing, while bacteria levels have generally improved.

Other metrics, like chlorophyll levels, look bleaker: An indicator that there’s too much algae, which can be toxic to humans and cause fish kills, chlorophyll scored just 18% in harbor and Patapsco River testing.

The environmental nonprofit’s findings come after Waterfront Partnership, the group that’s led the movement to make the harbor swimmable, released rosier findings last fall.

While Blue Water’s reports focus on the health of the Harbor ecosystem — for underwater life like fish, crabs and plants — the Waterfront Partnership emphasized safety for activities like swimming and kayaking.

“We know it’s a mixed bag. The harbor has good days. The harbor has bad days,” said Adam Lindquist, the partnership’s vice president. “But we think overall we’ve seen improvement.”

Lindquist pointed to dramatic improvements in metrics like dissolved oxygen and nitrogen pollution over the last 15 years. He remains bullish.

Katie Pumphrey, the long-distance swimmer who ended her marathon swim in the Inner Harbor, is gearing up for another attempt next week, while Lindquist said Waterfront Partnership will hold another Harbor swim event in June.

Volpitta, whose group has monitored water quality in the watershed since 2009, said the “dark horse” impacting the water quality has been phosphorous pollution, which enters harbor with sediment, through industrial sources, stormwater and sewage overflows.

Phosphorous levels in the harbor and the Pataspco scored 48% in Blue Water’s testing, getting worse over the last decade.

One picture that has become clearer as Blue Water accumulates more data is a divergence between two harbor tributaries.

Over the last decade, key measures – for nitrogen and phosphorous pollution, turbidity and conductivity — have largely improved in the Jones Falls, which runs north to south through the city. Puzzlingly, Volpitta said, these same metrics have gone in the opposite direction in the Gwynns Falls, which runs through West Baltimore into the harbor.

Baltimore and Baltimore County have spent billions of dollars to better control pollution in the harbor.

Much of that investment has come since 2002, when Baltimore entered a consent decree governing its sewage system with the U.S. Environmental Protection Agency. Baltimore remains years away from completing work mandated by federal regulators with a revised deadline of 2030.

Baltimore’s Department of Public Works has also spent big on contractors to bring its Back River Wastewater treatment plant into compliance after pandemic lapses.

Across its wastewater system, Baltimore is projected to invest $2.1 billion in improvements between 2002 and 2032, said Jennifer Combs, a Public Works spokesperson, in a statement.

“Despite this extraordinary investment” there is still more to do, Combs said. Ensuring clean water goes beyond just DPW, she said, including improved land-management practices.

Volpitta said she’s not here to tell people whether they should or shouldn’t swim in the harbor, but to help them understand the risks.

Officials and advocates need to double down on stormwater infrastructure and enforcement of existing clean water laws, she said. “There’s no more time for half-measures.”