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Recent Heat Wave Turns Baltimore Inner Harbor Green

Late last week, the Jones Falls, a portion of Baltimore's Inner Harbor, turned a milky-green color, giving off a rotten-egg odor. Nearly 200 fish were found floating dead at the harbor's surface, and the culprit was the recent heat wave.

Although no record highs were recorded in Baltimore during the Northeast heat wave, temperatures were 3-10 degrees F above normal, reaching the 90s from July 15 through July 21. RealFeel® temperatures hit close to 110 degrees on multiple days for several hours in the late morning and afternoon, according to AccuWeather Meteorologist Alex Sosnowski.

This type of reaction is very weather dependent, according to Baltimore's Healthy Harbor Coordinator Adam Lindquist.

"Last year the entire harbor turned milky green, not just the Jones Falls, but all around the harbor. It depends on the weather, the tides and how hot each day is," said Linquist.

The recent heat wave in the Northeast, with its unusually high temperatures, catapulted a reaction called a thermal inversion. This reaction transformed the harbor's water color and killed all the fish, Lindquist explained to

A thermal inversion, in simple terms, is when water from the bottom of the harbor flips positions with the water at the surface. When water temperatures change dramatically, the harbor's warm water acts more like a lake than a river, Lindquist said.

"The water warms up quickly and does not move a lot. It stays stagnate and doesn't flow," said Lindquist. "When you have hot, stagnate water, the bacteria from the bottom comes to the surface. It happens in lakes all the time."

Following the high temperatures, this sulfur bacteria switches places with the surface water. When this bacteria is exposed to the air on the surface, it changes to a milky green color and gives off a rotten-egg smell. It also brings to the surface with it low oxygen levels, which stress the fish living there who depend on high oxygen levels for survival. Eventually, due to the lack of oxygen, the fish die.

"A harbor is an unhealthy ecosystem," said Lindquist. Similar to heat-related heath risks associated with elderly or already unhealthy people, because harbors are already unhealthy, events like thermal inversion take a greater toll on the harbor than they would in a healthy body of water, said Lindquist.

"When events like this occur in a healthy body of water they do not result in fish kills," said Lindquist.

While pollution was not the direct killer of the fish in this instance, it played a role. The pollution remains the harbor's biggest issue. The number one source killing the harbor's fish is polluted storm water, which increases during heavy rainfall or storms.

"Storm water run-off flows over hard surfaces, picks up a lot of pollutants and then pollutes the harbor," said Lindquist.

Sewage is also another major problem for the city and its harbor. With sewage parts over a hundred years old, sewage is frequently leaked into the harbor waters.

A large rain storm hit Baltimore within 24 hours of the harbor's deadly transition late last week, pushing the bacteria-infested water out of the Jones Falls. The harbor returned to normal the next day. However, it is only a matter of time before the harbor again reverts back to its deadly green state.

"Once we have another streak of hot days, this exact situation will occur again and again," said Lindquist.

To battle this predicament, Baltimore's Healthy Harbor, a waterfront partnership initiative, has installed 2,000 square feet of floating wetlands to date to help pull the excess of nutrients and pollutants out of the water to aid in making the harbor a healthy ecosystem.

This fall, the organization will partner with the Chesapeake Bay Foundation to bring 100 oyster cages to the harbor. Oysters feed off algae and can help in cleaning up the harbor's waters.

While heat, algae and pollutants pose harmful threats to the progress of achieving a healthy Baltimore Inner Harbor, the Healthy Harbor Initiative strives to make the Baltimore Inner Harbor fishable and swim-able by 2020.