Pesticide suspected to be cause of Clear Lake fish kill (2005-08-02)
Results of an investigation by the Minnesota Departments of Agriculture (MDA)
and Natural Resources (DNR) into a fish kill in Clear Lake at Waseca have
determined that a pesticide used to kill mosquitoes, which is highly toxic
to fish, was present in water samples taken following the incident.
An estimated 100,000 to 300,000 adult black crappies died suddenly in late
June.
"Permethrin, a pesticide used to kill mosquitoes, was detected in two of
three water samples taken from Clear Lake," according to John Peckham,
supervisor of the MDA agricultural chemical investigation unit.
Permethrin was applied to a substantial part of the urban Clear Lake
watershed on June 19 and June 20, approximately two days before the fish
kill was first reported.
A significant rainfall event that occurred approximately 12 hours after the
permethrin application took place is suspected of causing the pesticide to
wash into Clear Lake.
"The next step," Peckham said, "is for the MDA to review its investigation
and the DNR's investigation and make a final determination as to whether any
state or federal pesticide laws were violated. It is unclear at this point
whether it can be documented by the MDA that there is a direct
cause-and-effect link between a violation of state or federal pesticide law,
the mosquito control application and the black crappie kill in Clear Lake."
The DNR pathology analysis turned up no evidence of other possible causes of
death for the fish, according to DNR Pathologist Joe Marcino. "There was no
indication of any viral or bacterial pathogen that could have caused the
observed mortality. The tissue damage, consisting of substantial damage to
the gill filaments, accompanied by hemorrhaging of internal organs, was
present in all specimens examined. Damage as observed is consistent with the
effect of a chemical toxin."
Hugh Valiant, Waterville area fisheries supervisor, said "Even after losing
large numbers of adult black crappies, our fish population assessment done
during the week of July 18 sampled black crappies, along with other fish
species of high recreational value. Prospects for angling in Clear Lake
remain good."
The spraying was done by Professional Mosquito Control of Clearwater.
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