BALTIMORE — Dead fish were discovered floating in Baltimore's Inner Harbor Wednesday.
WMAR-2 News received tips about the fish, so we went to check it out for ourselves.
Our cameras captured footage of several fish dead in the water.
According to the Maryland Department of the Environment, thousands more were spotted between the Rusty Scupper and Science Center with others located near Piers 5 and 6.
"The total number estimated to have died is 24,000," said Jay Apperson with the Environment Department. "They are almost exclusively Atlantic menhaden, although several catfish, white perch and a couple blue crabs were also observed."
We asked Apperson and two other experts why this is happening.
While there doesn't appear to be a pollution problem in the water, each expert seemed to agree cooler temperatures are a factor, causing a rise in bacteria resulting in oxygen loss.
Here is how each expert explained.
Adam Lindquist, Vice President of Waterfront Partnership of Baltimore:
The fish kill is being caused by what’s known as a pistachio tide. Pistachio tides are caused by unusual changes in water temperature. Normally, in the Harbor and in any other body of water, you have warm water on the surface and cooler water beneath it. What’s happening right now is that cold nights have cooled the surface of the water to the point where the surface water got colder than the water on the bottom. Because colder water is heavier than warmer water, the two naturally want to switch places.
When that happens, the surface water is replaced with water from the bottom. We call this an inversion and it brings a naturally occurring bacteria up from the bottom and that bacteria basically sucks up all the available oxygen in the water so that the fish cannot breathe.
Jay Apperson, Maryland Department of the Environment:
The Maryland Department of the Environment is investigating a fish kill in the Inner Harbor. We are seeing no sign of a pollution event having caused the fish kill. We took water measurements that showed the Harbor is essentially depleted of oxygen. This is likely related to the cooler temperatures in recent days, which we know from experience can cause the harbor to “turn over.” By that, we mean the conditions cause the deeper water, which is depleted of oxygen, to come to the surface. Fish that can’t escape the area don’t survive the drop in oxygen. Most of the dead fish are juvenile Atlantic menhaden. Low dissolved oxygen levels killed the fish.
The National Aquarium:
Cool nighttime temperatures like those experienced throughout our region over the past several days cause colder, more dense water from the harbor’s surface to sink, pushing sulfur bacteria living on the bottom of the harbor to the surface, a phenomenon known as thermal inversion. Once these bacteria are exposed to sunlight in the morning, it performs anoxygenic photosynthesis—or photosynthesis without the production of oxygen. The result is a green—pistachio green—algal bloom which looks and smells odd, while also eating up dissolved oxygen in the water and not creating any oxygen to replace it, which in turn impacts aquatic animals.
On top of this, the harbor has also experienced a mahogany tide in recent days. Mahogany tides are a type of brown algal bloom caused by nitrogen and phosphorous runoff found within the water combined with a stretch of warm, dry days with little water disruption from wind or rain. These conditions are perfect for the creation of a brown algae that impacts how deeply sunlight can permeate the water’s surface. Too much of this alga produced too quickly under perfect conditions causes the water’s dissolved oxygen levels to plummet, depriving other marine life of the oxygen they must pull from the water to survive. This can lead to die-offs of animals like small fish and blue crabs, as observed around the Inner Harbor today.
Pistachio and mahogany tides are not necessarily an indicator of poor water quality. Rather, they are naturally occurring, often temperature-related seasonal phenomena which happen one-to-four times per year, lasting several days at a time after which water quality improves.
The Aquarium’s conservation team is noticing small animals taking shelter in the shallow channel of the Aquarium’s new Harbor Wetland habitat, which supplies oxygenated water through an aeration system. These aerators help increase localized dissolved oxygen levels during negative water quality events. Aquarium staff have reported seeing an uptick in animals in the channel since the arrival of cooler temperatures and the pistachio and mahogany tides.
