WILSON LAKE -- Leave anything in the water here for long and you'll retrieve something that is simply covered with zebra mussels.

"They've really exploded this year," said Tommie Berger, the Wilson fisheries biologist for the Kansas Department of Wildlife and Parks.

Pontoons supporting house boats are simply covered with the hard-shelled mussels, the bane of freshwater fisheries because they filter out food at the lowest of levels, competing with other lake-dwelling animals, many of which provide food for sportfish.

And, those sharp shells can cut anyone unsuspecting enough to venture into the water without something on their feet.

"Oh yeah," he said of problems with people fighting the sharp shells. "Late last summer, there were kids coming up with cut feet. They're going to have to use water shoes."

Even though zebra mussels first were found in Wilson in October 2009, its now apparent they were actually introduced into the lake sometime in either 2007 or 2008, Berger said, based on the virtual explosion of mussels that now are being found.

If they were introduced into the lake in 2008, he reasons, they would have had three growing seasons.

Zebra mussels are prolific breeders and have a three- to five-year cycle of expansion.

"All this tells us they were here longer than what we realized they were," Berger said.

What's not yet known, however, is if the mussels have been in Wilson long enough to be at the peak, in terms of population.

So far, the only lake that's hit that peak is El Dorado Lake, which was the first in the state to see zebra mussels.

Berger said the population there collapsed after hitting the peak, but it's not known if that's a result of water that gets colder in the winter or if a drawdown of water levels was responsible.

"El Dorado dropped to less than 5 percent of what they were," he said. "And have stayed at that level."

To the south, where winter water temperatures don't get quite so cold, mussel populations have rebounded.

"So far in Kansas, and El Dorado has had them the longest, when they crash, they stay at that crashed level," Berger said.

Because zebra mussels are filter feeders, they filter out nutrients and leave lakes cleaner -- and clearer -- as they peak.

"I don't know how they can make water clearer than what Lake Wilson is," he said.

That's why he's hoping that after mussels peak at Wilson, the numbers will drop precipitously and stay that way.

Lake Wilson also is a bit salty.

But, he said, every lake is slightly different.

"There's questions on how far down they'll go when they peak here," he said. "I'm hoping that what we've seen this summer is the peak. But I won't know until next summer.

Perhaps sooner, he allows.

There's a chance they'll know this spring when Jason Goeckler, KDWP's aquatic nuisances species coordinator, samples the water for veligers -- tiny, microscopic sized mussels.

"They can tell if they have peaked," he said. "We may know before fall whether they actually peaked or not."

That's when KDWP will have to decide how to react, if they're at all interested in lowering water levels to hit the mussels as hard as possible.

But with the Corps of Engineers calling the shot on water releases, and the sometimes difficult task of getting water back in the lake, Berger said that's going to be a difficult decision.

"Hopefully, we'll peak and be on the downhill slide," Berger said. "But we'll see."