The Maryland Department of Natural Resources (DNR) recently confirmed the presence of whirling disease in a delivery of 8,000 commercially produced rainbow trout that were stocked in several Western Maryland streams..
On May 11, DNR staff observed suspicious behavior in fish that had been stocked in the North Branch Delayed Harvest Area, Evitts Creek, Jennings Run and Sidling Hill Creek. They immediately ceased stocking activities and took samples for testing. Results of this sampling confirmed the presence of whirling disease.
The whirling disease parasite was introduced into the eastern United States from Europe in the late 1950s and is currently known to exist in 24 states. It was first discovered in Maryland in 1995 in the North Branch Potomac River.
Whirling disease is harmless to humans, but the parasite can be fatal to trout and is particularly harmful to rainbow trout.
According to Maryland DNR, hatchery resources cannot meet all the demand for stocked trout, so commercially produced fish are used to supplement spring trout stocking. Vendors that supply fish to the State are required to be certified disease free for three years.
source: MD DNR