Fish return to Lake Agnes - mystery of dead Alexandria fish remains unsolved
The quiet waters of Lake Agnes have beguiled outdoor enthusiasts for years.
Now, they are stymieing scientists.
February's Ice Fishing Challenge held on Lake Agnes brought an unwelcome surprise. Not one fish was caught and entered in the contest.
Then, in March, dead fish were found at the outlet of Lake Henry and reported to the Department of Natural Resources (DNR). Additional dead fish were found at Lake Agnes' inlet.
In mid-May, DNR electrofishing found few fish in lakes Agnes and Henry - just some carp and yellow perch in Lake Agnes, and a few walleyes and perch were found in Lake Henry.
A fire in January at the SunOpta plant was assessed for a possible role in the mysterious disappearance of the fish.
Questions of whether chemicals in the plant, ash, foam or chlorine in the water used to fight the fire affected the fish remain unanswered.
A sample of material from the SunOpta fire was analyzed and not found to be toxic to fish.
DNR Fisheries inspected the lake for dissolved oxygen after the ice fishing contest. It found sufficient oxygen present in the lake at that time.
"I don't know that we are going to determine the exact cause," said Dean Beck, area supervisor at the Department of Natural Resources Fisheries Division. "What is positive is it was a partial fish kill and not a complete event."
"In terms of the suspicions about the fire and chemicals, I don't know that that's valid because it occurred upstream, too," Beck said. "There just isn't any smoking gun there."
Beck believed low oxygen concentrations were the most likely cause of the fish deaths.
"Thickness of ice and probably more than anything, the amount of snow cover that does not let sun penetrate, and the duration the ice was on," Beck offered as a possible explanation. "It was a tough winter kill and we had a fair amount of winter kill in our shallow lakes."
Treated water released from Alexandria Lakes Area Sanitary District was also analyzed as a possible cause.
Beck said the discharge from the sewage treatment plant into Lake Agnes "may have been a positive" factor.
The discharge contains oxygen, Beck explained.
"The fish kill would probably have been severe in absence of that plant," he said.
Just when all seemed lost, a netting assessment conducted by the DNR in early June rejuvenated hopes for fisherpeople.
"It looked much better than anticipated," Beck said about the netting results in Lake Agnes. "We saw all the common game fish that should be there; and a little better numbers than we might have anticipated - bass, bluegill, smaller crappie, a few larger northern pike and some yellow perch."
Is the problem continuing? No, judging from the netting.
"I was pleased with what I saw," Beck said. "It wasn't out of line with what we see on a lot of different surveys."
The netting survey in Lake Agnes revealed four walleyes per gill net; blue gills from 4.5 inches to 7 inches long; northern pike 17 to 25 inches; yellow perch 5 to 8 inches; and smaller black crappies.
"I truly anticipate the game fish population will rebuild," Beck said.
Is it time to haul out the fishing poles?
"I don't think the numbers will be as high as they were, but it's certainly worth fishing again," Beck said, but he advised, "We are just wanting people to keep the small fish."
PROTECTING THE LAKES
"It does highlight the need to look at what is going in the lake," Beck said.
What solutions are available to keep the lakes safe from pollutants and other harmful entities?
Storm water runoff and treatment to lower the amount of nutrients and sediments in the water are areas that could be addressed, Beck said.
For example, Beck said the foam used for firefighting fires near water could be assessed.
"There are other compositions of that foam that could have less oxygen demand," he said.
Beck noted the construction of containment ponds in Alexandria below industries are designed to intercept pollutants before they reach the lake.
He also mentioned the recently added stormwater retention basins and the collection and treatment occurring in the southern portion of the city.
"The city of Alexandria has been ahead of the game," Beck said. "I see progress."