About 2,000 dead fish found floating on the surface of a small Forest Hill pond in Friends Park north of Bel Air last Sunday died from a complex natural process and possibly improper pond management, a state official said.
Walter L. Butler, a state natural resources manager, visited the pond Sunday, took water samples and inspected the site.
He told county officials that his test results indicated that overstocking, warm water temperatures and normal bacteria growth had killed the bluegills.
Deputy Chief Larry Mabe of Harford County's Division of Emergency Operations said the pond was not polluted and that the only serious problem was the stench from the dead fish, which prompted a cleanup along the pond's shore.
Robert Staab, parks and recreation director for the county, promised that his department would try to prevent a recurrence of the incident.
Deputy Chief Mabe was on duty Sunday at 10:45 a.m. when his office was alerted to a large-scale fish kill involving small bluegills at Friends Pond on Jarrettsville Road east of Route 24.
Friends Pond, about one-fourth to one-half acre in size, is one of six such ponds run by the Parks and Recreation Department. Fishing is permitted at all except Edgewater Village Parks on Brookside Drive in Edgewood.
"We called in officials from the state department of the environment, the county Health Department and county Parks and Recreation to assist in determining the cause," Deputy Chief Mabe said.
Charles A. Poukish, another state natural resources manager, said he concurred with Mr. Butler's findings.
"No one factor causes it," Mr. Poukish said. "The important thing to know is that you just can't toss fish into a pond and expect everything to be perfect. Ponds need proper management or you are going to have situations like this."
Mr. Poukish cited several other factors that can contribute to the demise of fish, including a possible imbalance in the water's acidity.
"All of the factors place a certain amount of stress on a species of fish," he said. "When that stress becomes too great, the fish begin dying."
Deputy Chief Mabe said the parks and recreation staff handled the cleanup.
Other fish, including catfish, trout and possibly bass, inhabit the pond, the deputy chief said.
Mr. Staab said his staff has no "experts on ichthyology" to manage the ponds.
"We generally call the Fisheries Division of the state Department of Natural Resources about such things as stocking ponds," he said.
Barbara MacLeod, a DNR spokeswoman, said the freshwater fisheries division stocks ponds each spring.
She said that 100 pounds of catfish were put into the Friends Park pond last month for a fishing derby and that the pond had been stocked with trout in the spring.
Mr. Staab said he would check to see if DNR continues to routinely test the water before it stocks a pond.
"If not, we'll have all our ponds tested to prevent this -- if it is preventable -- from happening again," he said.