Millions of dead fish have washed up along the shores of the Chesapeake Bay over the past week, according to the Maryland Department of the Environment.
Officials are investigating the fish kill but say that according to preliminary results the cause was likely stress from unusually cold water temperatures.
"Our theory is that it was a very rapid temperature drop," MDE spokeswoman Dawn Stoltzfus said. "Obviously, these are fish that are susceptible to very cold temperatures."
Surface water temperatures reached about 0.5 degrees Celcius in December, the coldest on record in 25 years of monitoring, according to data from the Maryland Department of Natural Resources Bay Program.
The dead fish are mainly juvenile spot fish, just 3 to 6 inches in length. Officials say about 2 million dead fish have been found.
"I freaked out," said Dorothy Hopson, a resident of Stevensville, Maryland. The beach near her home was covered with dead fish.
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"I hate seeing anything dead. It was really nauseating."
Stoltzfus said reports of the fish kill started coming in last week from Calvert County and Kent Island.
The MDE said it was monitoring water quality in the area.
"So far, there don't appear to be any water quality or pollution issues that have contributed to this fish kill," Stoltzfus said.
The last time there was a fish kill of this magnitude in Maryland was in 1976, when similar conditions led to 15 million dead fish in the bay.
NBC News station WBALTV and msnbc.com staff contributed to this report.