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Posted 6/19/2017

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By Jennifer Thomason, Jade Young and Zac Wolf, Louisville District Water Quality Team


On January 3, 2017, Deryck Rodgers, manager, Nolin River Lake, Bee Spring, Kentucky, contacted the Louisville District water quality team to report an ongoing biological event unlike anything previously observed at the lake. What originally appeared to be an oil slick turned out to be millions of tiny animals, scientifically categorized as zooplankton. The water quality team quickly engaged other water quality programs in the Great Lakes and Ohio River Division to determine if any sister districts were familiar with the type of bloom event described by the lake staff.

The Huntington District water quality team volunteered to assist in a field investigation. Louisville District biologists Jennifer Thomason and Zac Wolf organized the field investigation, coordinating with Huntington District water quality team members Steve Foster and Thaddeus Tuggle, as well as the Kentucky Division of Water (KDOW), U.S. Geological Survey Kentucky Science Center, U.S. Army Engineer Research and Development Center, Nolin River Lake Ranger Libby Watt, and BSA Environmental Services, Inc.

During the field investigation, biological, physical and limited chemical data were collected by the Louisville and Huntington water quality teams. USGS collected physical, nutrient and biological samples. Watt explained the conditions in which the bloom was first observed and the initial response efforts by the KDOW and Kentucky Environmental Response Team. Watt also provided the extent of the bloom, which KDOW identified as a type of water flea.

Biological samples were sent to BSA for full characterization. The results from this analysis and the resulting conclusions are what make this event a remarkable phenomenon. BSA determined that the sample was dominated by Daphnia lumholtzi, an invasive species that is native to Africa, Asia, and Australia and was only previously known to occur in the Cumberland River drainage in Kentucky. The overwhelming scientific documentation on this species in the U.S. states that the species prefers temperatures warmer than our native Daphnia species. So why was this invasive water flea blooming in a Green River Basin lake during winter?

Initially it was thought that the bloom occurred in response to increased growth in algae—the primary food source—after a precipitation event. However, the short duration of the algae growth and cold temperatures would not likely have driven a bloom this size of D. lumholtzi. Further, this species typically has large spines from the head and tail during feeding blooms as a defense to becoming fish food. The organisms in the sample provided to BSA contained small spines and the females were carrying eggs, indicating that this was a reproductive bloom—not a feeding bloom. There are currently no indicators in the scientific literature or in the other data collected during the field investigation to determine why a large reproductive bloom of D. lumholtzi would occur in Nolin River Lake during winter.

The Louisville District water quality team has documented the occurrence in the district’s files and continues to investigate the available literature on the species to garner any additional details that may help to understand this event. Through inquiry with the experts at BSA there are no concerns that the species may affect water quality conditions at the lake and the species has not been documented to have adverse effects on the lake ecology. The bloom dissipated by January 5, 2017, and no other D. lumholtzi blooms have been reported since.