Rose Lake out of luck
Despite their best efforts, officials with the Department of Natural Resources were unable to eradicate zebra mussels from Rose Lake this summer as they had hoped.
"We knew that these treatments were something that has never been tried before, so we were cautiously optimistic on their outcome," Nathan Olson, DNR invasive species specialist, said. "However it is a method we believed was a good attempt but we will be cautious about trying it again in the future."
Last fall, DNR biologists investigated two separate cases where boat lifts used in zebra mussel-infested lakes had been moved to non-infested Rose Lake in Otter Tail County between Frazee and Vergas, and Lake Irene in Douglas County.
According to a DNR press release: "In both lakes, only juvenile zebra mussels were found in a small, localized area. This offered the DNR the unique opportunity to attempt to eradicate zebra mussels by treating both areas with copper sulfate, a common chemical used to treat snails that cause swimmers itch."
With the attempted treatment, DNR biologists collected water samples to look for larval zebra mussels and conducted scuba and lake equipment searches to look for juvenile and adult zebra mussels throughout the 2012 open water season.
"We did not find any veligers (larval zebra mussels) in our water samples or large zebra mussels during our scuba searches this summer," Olson said. "However, during our fall searches, we did find adult zebra mussels in both lakes."
Olson added that because monitoring efforts did not produce any veligers or juvenile zebra mussels, the DNR cannot confirm that zebra mussels have reproduced in either lake. The recent find of adult mussels means that despite early detection and a rapid DNR response, efforts to kill the zebra mussels in these lakes were not successful.
"We are not planning to do any follow-up treatments," Olson said. "The zebra mussels that we found this year are larger than last year, which makes them more difficult to kill. We do not feel it is financially prudent to spend more money on a treatment that did not work the first time."
But, the DNR will still continue to monitor the lakes and evaluate the development of zebra mussels.
"We will be continuing to do veliger sampling, which is taking water samples and looking young larval zebra mussels and snorkel or scuba and dock and lift surveys to look for adults/juveniles," he said.
Rose Lake and Lake Irene aren't the only two lakes hit either. The aquatic invasive continues to spread
Early last week, the DNR confirmed the presence of zebra mussels in Lake Miltona, located north of Lake Carlos and downstream of Lake Irene.
The DNR has also confirmed that zebra mussels have been found in the Ottertail River below Orwell Reservoir. Low water levels revealed zebra mussels of various sizes attached to rocks and debris.
"The presence of zebra mussels below Orwell Reservoir is not surprising as these zebra mussels were found downstream of where the Pelican River enters the Ottertail River," Olson said. "Zebra mussels were discovered in the Pelican River and Pelican Lake near Pelican Rapids in September 2009."
The DNR has since seen zebra mussels move downstream into Lizzie and Prairie lakes, and it now appears they have found their way into the lower Otter Tail River.
Because zebra mussels have been found in all these waters, they are now listed as designated infested waters.
The DNR has confirmed that water samples taken late this summer from Kerbs, Paul and Rusch lakes in Otter Tail County contained zebra mussel larvae (veligers) as well.
Other infested lakes
In association with a proposed water outlet project, the Little McDonald, Kerbs and Paul Lake Improvement District contracted with RMB Environmental Laboratories, Inc. in Detroit Lakes to collect an August water sample from Little McDonald, Paul, Rusch and Kerbs lakes.
The proposed water outlet project would address high water issues in the surrounding area by connecting these lakes to several other lakes before the water enters the Ottertail River system.
"High water in this area has caused damage to shorelines, property and roads," said Roger Neitzke, president of LMKP-LID. "At present, there is no outlet in the area to alleviate this problem."
One of the conditions of outletting the water was that if any aquatic invasive species were found, the outlet (which has not been constructed yet) would be closed. This prompted the LMKP-LID to voluntarily test the lakes for zebra mussel veligers as a precaution, prior to construction.
As part of their protocol, RMB Labs contacted the DNR with the veliger findings.
The samples were sent to the New York State Museum, which verified the presence of zebra mussel veligers. No adult zebra mussels were found after DNR biologists inspected hundreds of docks and boat lifts in these waters.
"At this time, we aren't sure where the adult zebra mussel population exists," Olson sad. "It is surprising that no veligers were found in water samples taken from Little McDonald Lake although it connects with the three lakes where veligers were found."
Although adult zebra mussels have not been verified, the DNR will take a precautionary approach by designating all four lakes as infested waters.
Follow Pippi Mayfield on Twitter at @PippiMayfield.