Freshwater ‘River’ Found Flowing Within Gulf Stream : Mississippi: Summer’s flooding has affected the ocean off Florida, researchers find. But they expect it to be temporary.

Oceanographer Rod Zika and colleagues were on a boat 10 miles off the Florida coast, studying waves and currents for research on oil spills, when they found something they weren’t expecting: a whole lot of fresh water.

They discovered that the devastating summer floods in the Midwest are being felt 1,500 miles away. The Mississippi River’s waters are flowing around Florida and into the Atlantic Ocean in a freshwater river at least 10 miles wide that is carried by the Gulf Stream.

“What we observed as a result of that water was a dramatic change in the chemistry and the biology off the south Florida coast,” Zika said. “We’ve never seen this dramatic an effect on it along the Florida coast before.”

One result: Parts of the Gulf Stream, normally deep blue off southern Florida, are instead dark green.

The effects of all that fresh water on marine life aren’t clear, however.

Fish may not be killed but might move to water with higher salinity. Area fishermen have reported having to head miles farther out to sea, past the Gulf Stream, to get normal catches.

The fresh water carries pollutants, such as hydrogen peroxide, pesticides and oils. “In another way, it has a lot of nutrients; that can cause dramatic increases in amount of productivity in water,” Zika said.

“It may start to grow organisms you don’t want to see, such as red tides, which can cause fish kills and produce toxins that get into the food chain, and into shellfish. It can affect lobster and fish larvae. These organisms don’t do well in fresh water.”

But because the Gulf Stream moves rapidly, the fresh water can be expected to disperse to the high seas, probably minimizing the effects in any one area, Zika said.

“This will all return to normal. This is a temporary state,” he said.

Zika and colleagues from the University of Miami’s Rosenstiel School of Marine and Atmospheric Science found the floodwaters while on a week’s working cruise studying wave formations and currents between Miami and Key West and out into the Florida Straits toward Cuba. They were doing research for the U.S. Navy and the Coast Guard on the probable directions oil spills would take.

The amount of salt in the Florida Current, as the strip of the Gulf Stream passing the Florida coast is known, normally registers 36 parts per thousand this time of year, Zika said.

“We found salinities that ranged from 31 to 32 parts per thousand, very consistently,” said Zika, a professor of marine and atmospheric chemistry. “In order for that reduction to happen, you have to have an enormous influx of fresh water from someplace.”

The Mississippi’s normal outflow into the Gulf of Mexico, he said, is very small compared to the flow of water in the Gulf Stream. But now, there are signs of the river’s fresh water in an area 10 to 12 miles wide and more than 60 feet deep, he said.

Among the signs are the Gulf Stream’s color change, because of an enormous amount of dissolved organic material from the Mississippi and rivers that feed into it.

The sea water also carries a lot more organic life than usual, the researchers discovered. “The nature of the organisms that were observed . . . were more closely related to organisms that are found in coastal regions or in estuaries,” Zika said.