Zebra mussel discovered in Iowa Great Lakes

SPIRIT LAKE, Iowa -- Since this spring, sampling plates have been dangling from the bottom of navigation buoys throughout the Iowa Great Lakes so Department of Natural Resources staff can monitor for the appearance of zebra mussels, an invasive species that has plagued bodies of water not just in Iowa and Minnesota, but throughout at least 29 states across the U.S.

Clear plates throughout much of the summer were a positive sign, but that ended on Sept. 5, when a sampling plate pulled from Upper Gar Lake off the southern tip of East Lake Okoboji had a solitary juvenile zebra mussel attached to the underside of a plate.

The zebra mussel, about the size of a toddler's thumbnail, is now in a labeled jar at the Spirit Lake Fish Hatchery.

Mike Hawkins, a fisheries management biologist with the Iowa DNR, said the discovery has resulted in stepped up monitoring efforts and public education about the aquatic invasive species.

Aside from the human impact from zebra mussels -- their sharp edges can cut bare feet and toes, and they can clog the water pipes of municipal plants that get their water supply from the lake -- the invasive species can cause ecological devastation.

"They will change the food chain dramatically in the lakes," Hawkins said. "They're a filter feeder, and an adult can filter up to a quart of water a day."

In some extreme cases, adult zebra mussels can reach a density of 6,000 per square foot.

"You get these massive numbers out there and they can filter a water body clean, eating plankton and algae," he explained.

That food source is the same that native fish species rely on for survival.

"You can have some increases in blue-green algae as well," Hawkins said. "Zebra mussels don't eat cyanobacteria."

As for what feeds on the zebra mussel, freshwater drum fish and breeds of diving ducks are the most likely to eat them, but they don't consume enough to control the prolific reproduction efforts of the invasive.

"Our only tool against zebra mussels is prevention. Once they've infested a water body, there's very little that can be done," Hawkins said.

Upper Gar isn't the first Iowa lake to report the discovery of zebra mussel. Clear Lake, located two hours east of the Iowa Great Lakes, is infested, and the Mississippi River, which flows along Iowa's eastern border, has been infested for many years. Those infestations have led DNR staff from around the state to keep a watchful eye on the lakes in their neighborhood.

"We've definitely been watching for them for quite some time," Hawkins said of monitoring efforts in the Iowa Great Lakes.

Zebra mussels can be spread a couple of different ways -- an adult attaches to a boat or trailer (something that's been in the water) and detaches when that boat has been put in another water body. The zebra mussel can survive out of water for up to five days, so it's still possible to spread the aquatic hitchhiker just by boating in different lakes on the weekends.

"The other way, probably more typical of how they are transported, is as a veliger, in their larval form," Hawkins said. Veligers are microscopic and cannot be seen without the aid of a high-powered microscope.

"There can be many, many of these in just a small amount of water," he explained. "Bilge water, water left in a live well or a bait bucket, anything that's coming out of an infested water body is going to have veligers in the water.

"Our mantra is clean, drain and dry your boats and equipment," Hawkins said.

The Iowa DNR recommends letting boats, jet-skis and other watercraft dry for at least five days between lake visits. In cases where five days isn't an option, people should thoroughly wash the watercraft with a pressure washer and use a disinfectant in the bilge tank.

"What we've found in Iowa is most boaters ... know about aquatic invasive species," said Hawkins. "Our educational campaign in Iowa has really worked."

While Hawkins said some constituents want the Iowa DNR to police every single boat going into every single lake in the state to check for aquatic hitchhikers, that's simply not feasible. At the Spirit Lake Fish Hatchery, however, Hawkins said there were seven boat ramp inspectors working just in the Iowa Great Lakes this summer. The inspections, often done Friday through Sunday, were performed by temporary employees and unpaid summer interns who also worked to educate boaters about invasive species.

As for the zebra mussel that was found in Upper Gar Lake, Hawkins said there are two possibilities on how it arrived there. The first is that it came from a veliger released by a boat through a bilge tank. The second, which Hawkins said is bleaker, is that it came from an adult in the lake.

"We have not been able to find any adults, but we're right at the beginning stages of looking," he said. The two to three dozen sampling plates spread throughout the Iowa Great Lakes this summer is hardly enough to know whether more zebra mussels exist.

"A better sample of substrate is going to be this fall as these docks and hoists come out of the water," Hawkins said, adding that information will go out to lakeshore home owners yet this fall explaining what to look for on their equipment.

"You shouldn't see adults on a hoist," he said.

As boat owners inspect their equipment, Hawkins said DNR staff will be out looking for zebra mussels along shorelines, rocks and around bridges.

"The best case scenario is that this was an introduction (of veligers) and it was spread out," he said. "If they're not close enough to reproduce, it would be a non-viable population."

Daily Globe Reporter Julie Buntjer may be reached at 376-7330.

1/2: No bigger than a toddler's thumbnail, this juvenile zebra mussel was discovered on a sampling plate in Upper Gar Lake earlier this month.

2/2: This fishing rod and reel, pulled from the bottom of Clear Lake in Iowa, is littered with zebra mussels.