To the editor:
As many of you may have seen or heard by now, we recently had a significant fish kill at Swan Lake. The fisheries biologists from the Iowa Department of Natural Resources (IDNR) were here over the weekend to run various tests.
To sum up their findings: the available oxygen levels in the water became too low due to the natural processes associated with large blue-green algae blooms. The biologists will be back early this fall to do more fish sampling. At that time, they will get an idea of population levels and determine if re-stocking will be necessary.
Most all fish species and ages were affected. A silver lining in this unfortunate event is that at least 65 grass carp died, as well. When the lake was lowered 3 years ago, we removed as many as we could, nearly 50, but had hoped for more. Grass carp were introduced to the lake after killing it off to remove common carp, approximately 13 years ago.
Since then, the IDNR has learned that grass carp actually have a negative affect on a fishery. Looking forward, not having as many grass carp will benefit Swan Lake by not having these herbivorous fish to eat rooted plants or stir up sediment off the bottom of the lake.
Remaining fish are okay to catch and to eat. There is nothing toxic with the fish. They simply did have enough oxygen to breathe. Anytime blue-green algae is present, it is recommended to avoid contact with your skin.
The beach near the East Shelter is currently closed as we deal with fish carcasses present.
Blue-green algae is not a new organism. According to fossil records, it has been around for more than 3 billion years. The difference we see in blue-green algae today is that it has an unnatural amount of food available. Swan Lake has one of the highest levels of phosphorus and other nutrients of any lake in Iowa.
This event should be a good reminder to all of us that often times we don’t immediately see the negative impacts our actions have. The water condition at Swan Lake, as well as most other lakes, ponds and rivers in Iowa, is a result of decades of land use in the Swan Lake Watershed that didn’t keep long-term results or big-picture concepts in mind.
Choices we make today may not have obvious results, but our children and grandchildren will certainly be dealing with them, just as we are today dealing with impaired waters. Will there be any lakes in Iowa that can sustain healthy fish populations in 50 years?
The answer starts today with choices we make. Support land owners who make conscientious choices for a better tomorrow, and share this with those who you think could do better.
Please feel free to share this with any of your friends who may be interested in what’s happening not just at Swan Lake right now but at a body of water near their home as well.
Carroll County Conservation Board, Carroll
