October 26, 2006
On Tuesday and Wednesday of this week (Oct. 24-25), the
Department of Natural Resources (DNR) coordinated a helicopter
assault on the carp population in Swan Lake, which is located in
Two helicopters owned and operated by Teri-John Aviation out of
St. Peter delivered some 3,880 gallons of liquid rotenone to
nearly 3,000 acres of water remaining in the lake.
"We're extremely hopeful that the rotenone will kill the vast
majority, if not all, of the carp that have been reproducing in
Swan Lake," said Ken Varland, DNR southern region wildlife manager
at New Ulm. "If any do survive, however, we're banking on Mother
Nature to produce winterkill conditions that will eliminate them."
Varland said "tens of thousands" of dead carp were already
observed by Wednesday afternoon.
Carp, a species not native to North America, root up aquatic
vegetation, causing turbidity and other water quality problems.
Eventually, if left unchecked, carp-infested waters become
intolerable for other fish species and water-dependent wildlife
such as waterfowl.
Rotenone is a naturally occurring extract derived from the roots
of various tropical plants. While the product is safe to humans
and most species of wildlife and domestic animals when applied
according to label instructions, it is deadly on gill-breathing
animals such as fish.
Varland said rotenone has been used effectively for years to
eliminate carp from wetlands and shallow lakes. It is believed,
however, that the Swan Lake project is the largest of its kind in
Minnesota, if not the nation. At 10,000 acres (15 square miles),
Swan Lake is considered the largest prairie pothole marsh in the
"We were alarmed when the presence of carp was verified in Swan
Lake in November of 2005 and knew immediately that we had to do
everything in our means to get rid of them," Varland said. "And
when we explained the dire situation to Swan Lake duck hunters and
others, they immediately got behind us, even though they knew that
would mean very limited duck hunting access this fall."
The DNR plan called for immediately lowering water levels in the
lake as much as possible and then treating any remaining water
with rotenone just prior to freeze-up this year. Minimizing the
amount of water needing to be treated serves several purposes: it
lessens the cost, increases the probability of a complete kill,
creates conditions more conducive to a winterkill and promotes the
growth of beneficial aquatic vegetation.
Varland said helicopters began spraying rotenone on the lake about
noon on Tuesday and continued until dark. They then resumed again
at mid-morning on Wednesday and finished up early in the
afternoon. An ice cover both mornings delayed the start of the
application, forcing a continuation into the second day.
"This was an extremely complicated project to carry out,
especially since the rotenone application came during the duck
season," Varland said.
With some 130 duck hunting cabins and numerous other access sites
to the lake, Varland said extra measures were taken to keep people
off the water during the actual application. Public notices were
sent out, signs posted and DNR staff stationed at all potential
More than 50 DNR staff from various divisions participated in the
project. "The logistics involved in something like this is
amazing," Varland said. "Staff from the Nicollet area wildlife
office, particularly Kristy Zajac who coordinated the project and
ran the command center, did an outstanding job pulling this all
together. And the support we got from other DNR divisions was
And now it's Mother Nature's turn, Varland said. "We've done
everything within our means to protect the fabulous treasure that
is Swan Lake. Now, if we get the winterkill conditions we're
hoping for, our expectation is that next spring we'll find all the
carp are gone and the lake being replenished by snow melt and the