Bacteria Bloom Triggers Foul Stench at Baltimore's Inner Harbor

On October 3rd, 2025, Baltimore's Inner Harbor is experiencing a familiar problem - a putrid stench that has locals and tourists alike holding their noses. According to the Maryland Department of the Environment (MDE), this is part of an annual turnover event caused by the weather.

The drastic change from daytime to nighttime temperatures has led to surface water cooling and sinking to the bottom of the harbor, causing bacteria from the floor to rise to the surface. This process, known as "upwelling," is common in lakes but is not typical for the harbor, which has become stagnant due to dredging.

The resulting bacteria do not require much oxygen, and their sulfur-like byproduct creates not only the unpleasant smell but also a green hue in the water. Residents in the area, such as Lauryn Allen of Fells Point, have been quick to notice the issue, with one describing the smell as akin to "an unfortunate tray of deviled eggs that's been left out for a really long time."

This is not the first time the harbor has faced such a problem. Last week, the MDE estimated that there were 25,000 dead menhaden fish in the water, likely due to low dissolved oxygen levels caused by the seasonal die-off of algae. While the MDE does not believe this was caused by pollution, the recurring issues have left locals and tourists alike feeling "ashamed" and "embarrassed" about the state of Baltimore's most prized tourist spot.

The National Aquarium has suggested that a long-term solution to the problem may be to raise the harbor's floor, allowing for better water flow and preventing these thermal inversions from occurring. Until then, residents and visitors alike will have to endure the unpleasant smell, which is likely to persist until a soaking rain or front can clear the air.