By Suzi Parker
LITTLE ROCK, Ark (Reuters) - Wildlife officials have discovered thousands of dead fish along the Arkansas River in Little Rock and were still counting carcasses on Tuesday, a day after an angler reported seeing dozens of dead white bass.
"We are on the river trying to determine the extent of the fish kill," said Keith Stephens, public information coordinator for the Arkansas Game and Fish Commission.
Wildlife investigators said the dead fish were mainly white bass, which are common in the river, and were between 5 and 8 inches long. Most were found near the foot of the Two Rivers Bridge, an 80-foot pedestrian bridge that opened in July.
An Arkansas Department of Pollution Control and Ecology official said toxins had not been eliminated as a potential cause and that oxygen levels had tested normal so far. Other test results for disease and parasites could take a month to conclude.
In late December, thousands of freshwater drum and yellow bass died in the Arkansas River. A month later, 500 more drum died. Officials later determined that the fish kills were likely caused by increases in atmospheric oxygen and nitrogen in the water after spillway gates were opened.
The massive winter fish kill had appeared especially alarming because it occurred around the same time thousands of red-winged blackbirds dropped dead from the sky on New Year's Eve near Beebe, Arkansas.
Studies later concluded that the birds died from blunt force trauma possibly caused by unusually loud noises.
Fish kills are not uncommon, according to the game and fish officials, and are often caused by reduced oxygen in the water, algae bloom or overpopulation. Infectious disease, parasites and toxicity can also cause fish kills.
Stephens said that because Monday's discovery was in a different location from the fish kills last winter, the white bass deaths were unlikely to be caused by gas bubble trauma.
Seasonal changes in water temperature can also cause such deaths, officials said.
(Edited by Karen Brooks and Cynthia Johnston)