Statement on the Baltimore Harbor Pistachio Tide

Oct 15

Written By Adam Lindquist | Vice President

Pistachio Tide in Baltimore’s Inner Harbor 2025

The following remarks were delivered by Adam Lindquist, vice president of the Waterfront Partnership, during the release of the Healthy Harbor Report Card on October 10, 2025 to address the ongoing pistachio tide and persistent dead zone in the Baltimore Harbor.

“If the Baltimore Harbor were a patient, that patient has had a heart attack. While turnover events and pistachio tides are an annual occurrence, the geographic scope and duration of this pistachio tide is unprecedented in recent history.

On September 20th, dissolved oxygen levels in the Inner Harbor dropped consistently below 2 milligrams per liter — what scientists call a dead zone. Six days later, oxygen fell to nearly zero and has stayed there ever since. With no oxygen for two weeks, all living organisms have either escaped or perished — fish, crabs, shrimp, eels, all gone. With zero dissolved oxygen, the sulfide-rich, anoxic water and green sulfur bacteria from the bottom of the harbor have replaced the oxygen-producing algae and the bright green “pistachio tide” has lingered day after day. The Harbor isn’t recovering — it’s flatlining.

Estuaries are complex ecosystems — even more so when they’ve been engineered by people. The Inner Harbor, with its dredged channels and hardened bulkheads, has little natural shoreline left. It’s essentially a deep box of water. Because of this, we are seeing the pistachio tide impact the Inner Harbor but not other areas like the Middle Branch.

Last spring, by many measures, the Harbor was the healthiest it had been in living memory — full of rockfish, blue crabs, menhaden, even river otters. Blue Water Baltimore recorded the highest dissolved oxygen levels in fifteen years. But beneath the surface, a storm was brewing. Excessive algae growth, fueled by stormwater runoff and climate change, spread deep into the water column. When those algae died, they consumed oxygen, worsening the already low-oxygen conditions at the bottom.

By June, the deepest water was completely anoxic. For much of the summer, that layer stayed trapped — until late August, when cool nights triggered a violent turnover. The surface water sank, forcing oxygen-depleted water upward and killing nearly everything in its path. The effect was amplified by a long dry spell, which left no freshwater layer to slow the mixing.

In a typical year, pistachio tides resolve in a few days. But this year, the Harbor experienced what scientists call a regime shift — an abrupt, lasting change in how the ecosystem functions. Sulfur bacteria have taken over, producing the rotten-egg smell and locking the system into a low-oxygen state.

If the Harbor is a patient who is flatlining, it now needs the ecological equivalent of a defibrillator — a major pulse of oxygen to bring it back to life. That could come from a large storm flushing the system or from a combination of winds and tides that allow oxygenated water to return. When that happens, the Harbor will begin to breathe again.”