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Crystal Lake, Iowa – The Iowa Department of Natural Resources (DNR) confirmed last fall that Eurasian watermilfoil was growing again in Crystal Lake, located seven miles west of Forest City in Hancock County.
Crystal Lake had the first confirmed infestation of Eurasian watermilfoil in Iowa in 1993. It was treated with the aquatic herbicide Sonar in 1994, and no Eurasian watermilfoil had been found in the lake after that treatment, until it was found along the north shore last fall.
Another aquatic invasive plant, curlyleaf pondweed, is also growing throughout the Crystal Lake.
The DNR will use Sonar again this month to treat the Eurasian watermilfoil. It will take about 60 days after treatment for all the plants to die. If plants are killed too quickly, the mass of decaying plants will rob the water of oxygen and could cause a fish kill.
There are no restrictions on fishing or swimming with the use of Sonar. This treatment should also kill curlyleaf pondweed plants that are currently in the lake, but it will not prevent turions from growing later in the year.
Eurasian watermilfoil reproduces by fragmentation, which means small pieces of it grow into new plants. This makes Eurasian watermilfoil easier to control than other aquatic plants that grow from seeds or roots, because once the plants are dead, there are no structures left to grow into new plants.
Curlyleaf pondweed grows from turions, which are seed-like structures that are dropped into the sediment. Because turions can live for many years in the sediment before spouting, new plants can grow even after the current plants die.
“It is extremely expensive to control invasive plants with herbicides,” said Kim Bogenschutz, the DNR’s Aquatic Invasive Species Program Coordinator. “Preventing the spread of Eurasian watermilfoil and curlyleaf pondweed to other lakes is key because these plants are difficult, if not impossible, to get rid of once they get into a lake.”
“Boaters and anglers can unintentionally spread aquatic invasive species if they do not take the proper precautions - clean, drain, dry - after each time out on the water,” said Bogenschutz.
It is illegal to possess or transport prohibited aquatic invasive species, such as Eurasian watermilfoil and curlyleaf pondweed, in Iowa. Boaters must also drain all water from boats and equipment before leaving a water access and must keep drain plugs removed or opened during transport.
Find more information about aquatic invasive species and a list of infested waters in the 2019 Iowa Fishing Regulations booklet or on the DNR’s website at www.iowadnr.gov/ais.