"On Aug. 16, we experienced a sizable fish kill at Heron Pond at Three Creeks Metro Park," said John Watts Metro Parks Resource Manager. "It was felt early on that, given the numerous hot days and warm humid nights in July and early August and a very overcast day on Aug. 15, coinciding with an obvious algae bloom, all of which resulted in a a very low level of oxygen in Heron Pond led to the fish kill."
Watts said, with recent statewide concerns over blue-green algae and its by-products in many State Park lakes, Metro Parks felt that it was necessary to perform water testing to determine if any of these concerns applied to Heron Pond. Samples were collected and tested. Durning that same time, Enviromental Management Services completed cleaning up the dead fish on Aug. 17.
Watts said test results recently confirmed that both green and blue-green algae were present in the samples.
"Both of these are typically present in most pond samples," said Watts.
Further testing indicated two of the toxins of concern related to blue-green algae were also present, but in low enough concentrations to meet recreational exposure standards.
On Aug. 23, test results related to the oxygen levels were received. Watts said the important parameter is what is known as the Biological Oxygen Demand or BOD.
"Basically, this is a measure of the oxygen demand by all organisms within the system," said Watts. "A normal level for a natural water system is between .8 and 5 mg/liter. Anything above 6 mg/liter typically requires some treatment to maintain fish life. The result for Heron Pond was 105 mg/liter. This confirms that low oxygen levels were the culprit."
Metro Parks Resource Management staff will discuss management options to begin the recovery process of Heron Pond.
"As of right now, we would like for Heron Pond to remain closed until at least Aug. 27 to allow the upcoming cooler days and nights to help the pond with recovery (we should put up some temporary signage to inform daily visitors)," said Watts. "It is our hope Heron Pond can be re-opened for the weekend and we will confirm that in the next day or so."