Zorinsky Lake, a beloved Omaha refuge, is a ghost land now, drained of most of its water and blanketed in snow.
Barren, long-dead trees, caricatures of winter, stick up from the frozen basin. A long-submerged road has reappeared, a snowy path now leading nowhere.
The lake has become an open textbook on the turmoil that an invasive species can bring to an ecosystem.
Discovery of one tiny, clamlike invader in November triggered a chain of events that, within about a month, led to the draining of much of the lake's water. The lake could remain mostly empty into the fall or even another winter.
The zebra mussel is so pernicious, so prolific and so economically damaging that its arrival in the U.S. in the late 1980s led within a few years to the first significant national legislation tackling invasive species.
“It brings tears to my eyes. That lake was like a good friend to me,” said Omaha fisherman Terry Johnson. “It was our little jewel here in Omaha.”
Johnson is among some critics who point to failures elsewhere in combatting the mussel. They believe the draining of Zorinsky was undertaken too hastily.
Johnson said the lake had been filled with “game fish we saved for our grandkids.”
Scientists who have studied the mussel say it is tough to eradicate.
“I've got to give them credit for trying,” said Don Schloesser, research biologist for the U.S. Geological Survey and author of a book on zebra mussels in North America. “My gut feeling is that it ... is not going to work.”
Schloesser said remaining pools of water, niches in the Zorinsky lake bed and microenvironments can sustain the mussel.
“Sooner or later, the zebra mussel will come back,” he said. “If it doesn't come back internally, it will come from somewhere else, the same way it got there to begin with.”
The mussel most likely hitchhiked to Zorinsky on a boat that had been in infested waters elsewhere.
According to Mark D. Farr, who has studied invasive mussels for 10 years for the U.S. Army Corps of Engineers, draining Zorinsky was the logical choice. The corps owns the lake.
“De-watering and exposure of zebra mussels to freezing air temperatures can be a very effective control measure,” Farr said.
However, according to Farr, Schloesser and local researchers, lakes vary in their abilities to sustain zebra mussels. Reasons range from a lake's oxygen level to its temperature.
The 31 mussels found in Zorinsky raise an intriguing question about the Omaha lake's ability to sustain the species. Some of the Zorinsky mussels are as big as any found in the U.S., said Karie Decker, Nebraska's invasive species coordinator.
“That surprised us,” Decker said.
Their large size could mean that zebra mussels thrive in Zorinsky's waters, which would help validate the decision to drain the lake.
Or their size might mean that the lake isn't that hospitable, and it took several years for these zebra mussels to grow so big while not reproducing in significant numbers. Female mussels can produce 1 million larvae a year, with tens of thousands possibly surviving to adulthood.
Figuring that out “could be a piece of the puzzle,” said Dick Taylor, one of the Corps of Engineers officials leading the Zorinsky effort.
If Zorinsky's environment were inhospitable, that might have lessened the need to act so quickly.
Complicating the problem, scientists don't have the ability to assess the age of zebra mussels, which can live for two to five years.
What scientists do know is that the mussels from Zorinsky spent their entire adult lives in that lake. Mussels attach to a site in a lake or on a boat when they are still larvae, never again budging. It's at that site where they gain their shells and their clamlike appearance.
If the huskiest of Zorinsky's zebra mussels matured within a year, that would be an indication the lake is a friendly environment and Zorinsky could have been on the verge of a population explosion.
When that happens, teeming communities of mussels cement together, creating a shard-like covering on hard surfaces, clogging valves and pipes. They feed at the bottom of the food chain, which alters the fish population, often depleting key species.
Noting that there are many caveats, officials tackling the problem at Zorinsky say there are factors that could improve their odds of success:
›› Oxygen levels in the lake's water: Samples from Zorinsky have found, on occasion, locations where water deeper than 6 feet from the surface had too little oxygen to sustain zebra mussels.
That does not ensure that only the top several feet of the lake is the only portion where the mussel can live, but it increases the possibility. The lake is being lowered by about 17.5 feet, so there's reason to hope — if mussels only lived in the top 6 feet — that all the mussels were frozen to death this winter.
›› The aggressive lake-lowering: At other lakes where water levels were dropped to freeze out the mussel, the water level was not lowered by as much as at Zorinsky and was not kept down for as long.
Lakes in Minnesota and Pennsylvania, for example, were kept low for less than two weeks. Zorinsky could be kept low 10 months or longer.
The Zorinsky research team will study the lowered lake this summer to learn more about its zebra mussel population.
They'll search the exposed lake bed and remaining water for dead or living adult mussels. They hope to determine the depth in Zorinsky that mussels are found.
Additionally, they will sample the water for living larvae. If they find larvae, it will mean some adults survived the winter and had begun reproducing.
It could be possible for adults to survive the cold because a creek flows through Zorinsky and water in the remaining lake bed/creek is estimated to be about 15 feet deep. That water contains enough oxygen to sustain the zebra mussel, said John Hargrave, a biologist for the Corps of Engineers in Omaha.
What happens if live mussels or larvae are found?
“It's the $24,000 question,” said Dave Jensen, another corps biologist.
Other options have been considered and so far rejected as too costly or less likely to succeed.
Taylor said the team has a “pretty high expectation” they've done all they can.
Despite the uncertainty surrounding the efforts — and the loss of fish, turtles, snails and other aquatic life — officials say this was the right action.
“Most of us feel we wouldn't be doing our job if we didn't do everything we could to stop the zebra mussel,” said Daryl Bauer, fisheries outreach manager for the Nebraska Game and Parks Commission.
“There's going to be collateral damage, absolutely. We're aiming for long-term gain. If we've got a chance to do this at Zorinsky and keep them from spreading, we're going to do it.”