Aquatic plant blamed for fish kill
Published 12:00 am Tuesday, August 19, 2008
GATESVILLE – For Jay Greenwood, this week is much better than last.
Greenwood, Superintendent of Merchants Millpond State Park, and his staff are dealing with the aftermath of a fish kill that claimed the lives of approximately 125,000 fish.
“Things are going a lot better this week,” Greenwood said on Monday morning, six days after park rangers first spotted dead fish floating on the millpond’s surface.
That fish kill prompted Greenwood to close the millpond to canoeing and canoe camping. The pond encompasses 760 acres of the 3,296 acre park.
“We haven’t noticed any new masses of dead fish in the pond, so that’s an encouraging sign,” Greenwood said. “If nature will cooperate, we plan to reopen the pond later this week.”
Greenwood blamed parrot feather, an invasive aquatic species of plant life, for the fish kill.
“The plant is found in almost every body of water across the United States…it’s been larger than we’ve ever seen it this year here at the millpond,” Greenwood said.
So large, in fact, that Greenwood noted the dense surface mats, under which the plant grows, covered 20 acres in size.
“In previous years we’ve seen the plant growing near the base of trees,” he said. “When we noticed how large it had grown this year, we made plans to begin removing it by hand last week, but it then the plant died very unexpectedly.”
The plant’s death and resulting decay robbed the water of oxygen, which in turn led to the fish kill.
“It normally lives all summer and dies in the fall of the year with the first frost,” Greenwood explained. “When it died this year in the height of the summer months, it really caught us all off-guard.”
Greenwood said the resulting low levels of oxygen had the worst impact on the larger of the largemouth bass that live in the millpond.
“We saw larger bass turn-up dead than other species,” he said, adding that bluegill and catfish were also affected.
One saving grace was the unseasonably cool August nights the area experienced last week.
“With air temperatures in the lower 60’s at night, that cools the water temperature, which in turn adds more oxygen to the water,” Greenwood said.
Additionally, the park has ordered two aerators that will be used to increase the oxygen levels in the pond. Greenwood said those devices are rubber tubes containing tiny holes that will sink to the bottom of the pond where they will release air bubbles that will increase the oxygen levels.
Greenwood added that he is working with NC Wildlife Commission officials in an effort to orchestrate a restocking of largemouth bass in the millpond later this year as well as next spring.
“We still have good numbers of fish that survived this,” Greenwood stressed. “This is nothing compared to the aftermath of Hurricane Isabel (2003) where we lost over one million fish, about 90 percent of our stock. We recovered from that in five years. It will not take anywhere close to that long to recover from this latest fish kill.”
Meanwhile, North Carolina Division of Water Quality data indicate conditions in several of the state’s rivers may result in fish kills over the next few days. Organic rich water with very low dissolved oxygen levels from adjacent swamp lands is draining into significant portions of the Chowan, Pamlico, Roanoke rivers and other river systems in northeastern North Carolina. The result is areas with dissolved oxygen levels below what most fish require to survive.
In addition to Merchants Millpond, fish kills have been reported in the Chowan River near Winton and the Roanoke River near Jamesville.
Teams from the division are monitoring from Jamesville downstream to Bachelor Bay on the Roanoke River and near Winton and Tunis on the Chowan River. A fish kill at Tuscarora Beach, on the Chowan River, occurred earlier last week when an estimated 300-500 fish died. Oxygen levels, at that time, were measured at 0.55 milligrams per liter. In general, fish require dissolved oxygen levels near 3.0 milligrams per liter to survive, and levels near 6.0 to thrive.
“We have received additional reports of stressed and dying fish and our monitoring reveals low dissolved oxygen levels throughout the water column,” said Alan Klimek, DWQ division director. “The situation may take some time to right itself and, in the meantime, we could have some sizeable fish kills.”
Particularly sensitive are water bodies adjacent to wetland areas across much of the northeastern part of North Carolina.
The public is asked to report sightings of fish kills in the lower Roanoke and Chowan rivers to DWQ by calling the Washington Regional Office at (252) 946-6481. The division recommends that people not swim near or eat the dead and dying fish because of the risk of bacterial infection associated with fish decomposition.