Fish kills total 3.6 million along Neuse basin this year

So far this year, 3.6 million fish have died in the waters that make up the lower Neuse River basin. And for the most part, scientists can only guess why.

The figure surprises even the state's lead investigator on the Neuse. Last year, the Neuse River Rapid Response Team found 9,470 fish dead on the river.

"That's a huge jump," said Jason Green, the leader of the response team. "I hate to say we don't know what caused it, but in most of these cases, we are left gathering evidence 24 or 48 hours after an event, so 90 percent of the time, we have to guess."

The best guess right now is that the kills are the result of a combination of wild weather and a "nutrient-sensitive" river. That combination has led to a low oxygen-to-water ratio that the fish cannot handle.

Fish need five to eight milligrams of oxygen per liter of water to live. In the kills that the state has responded to, oxygen levels have dipped to less than one milligram per liter of river.

Hot weather is a kill factor, and tropical storm Hanna and the recent nor'easter may have also contributed to the kills. But part of the problem with finding a definitive answer is that some of the kills have occurred in areas where the state has no historical data.

The root cause may remain a mystery until scientists can respond to a kill as it happens.

"Generally, the Neuse River has a zone between New Bern and Minnesott Beach where fish kills occur," Green said. "We have monitoring equipment there and we do weekly monitoring on the Neuse, but we're finding more events occurring pretty randomly and in a pretty wide area."

Two weeks ago, a kill in the Cypress Lake community claimed 75,000 fish. But with no previous information from that area, state officials were left to guess that fertilizer from "manicured lawns" caused an algae bloom to grow faster than it normally would and suck oxygen from the man-made lake.

The most recent fish kills, both investigated Wednesday on creeks in Pamlico County, were also in areas where kills have never been reported to the state.

Those two kills, on Smith and Brown creeks, claimed nearly 2 million young menhaden.

"We've never seen that there, but that's not to say that there haven't been kills there," Green said. "There are a lot more houses in that area now to report them."

So far this year, the state has responded to 10 kills where more than 25,000 fish died. The Pamlico County kills this week are the largest by far.

During or after a fish kill, the state collects biological samples to see what kind of organisms are in the water. A more in-depth analysis of the nutrient content of the river is also done, but takes more time to process.

But those analyses don't always yield answers, Green said. "More data leads to more questions."