Baltimore harbor's water health is on the decline, new report shows
A new report found that the health of the water at Baltimore's Inner Harbor is on the decline, according to the 2025 Water Quality Data Report by the nonprofit Blue Water Baltimore.
The report found testing sites from downtown to Middle Branch showed poor to fair water quality.
After more than a decade of monitoring, the report showed concentrations of phosphorus are on track to deplete the harbor's ecosystem in years to come, according to our media partner, The Baltimore Banner.
"We can talk all day long about whether fair is good enough for the residents of Baltimore," Alice Volpitta, the Blue Water's harbor water-quality watchdog, told the Banner. "We have to start thinking: 'Is this good for the next generation or the generation after that?'"
Harbor quality report in 2025
In October 2025, a report was released by Blue Water Baltimore and Waterfront Partnership, showing that some areas in the harbor were improving and other areas were headed in the wrong direction. That data was compiled in 2024.
The annual update reports on the water quality and health of Baltimore's Inner Harbor based on data gathered by both Blue Water Baltimore and Waterfront Partnership in 2024.
The harbor received a "C" grade for overall ecosystem health. The report indicated ecological improvements and ongoing vulnerabilities.
Dissolved oxygen levels, a key measure of aquatic health, earned an "A" grading for the first time in the report's history. Waterfront Partnership says improved oxygen levels reflect major infrastructure upgrades and nutrient-reduction efforts across the region.
The report said that chlorophyll, an indicator of algae blooms, fell to a "D," its lowest mark since 2010. The report said nutrient pollution from stormwater runoff and wastewater continues to fuel algae growth that can block sunlight and deplete oxygen.
A strong stench at the harbor
In October 2025, there was a strong stench at the Inner Harbor.
The Maryland Department of the Environment (MDE) said the smell was because of an annual turnover event caused by the weather.
MDE said the drastic change from daytime to nighttime temperatures caused surface water to cool and sink to the bottom of the harbor, causing bacteria from the floor to rise.
These bacteria don't require a lot of oxygen. Officials said that at the surface, non-oxygenic photosynthesis takes place, and a sulfur-like byproduct creates not only the smell but a green hue.
The water turned green and had an "egg-like" smell.
A week earlier, the MDE said about 25,000 dead menhaden fish created a smell in the water from Canton to Locust Point.
Scientists with MDE said they measured low dissolved oxygen levels, and said this is likely due to the seasonal die-off of algae.