Cyanobacteria and other phytoplankton blooms have apparently increased as predicted since introduction of grass carp into Devils Lake. But it is not clear is that these blooms pose serious health risks to lake users. American mythology is full of stories about illness and death from “bad water.” Medical literature repeats warnings about exposure to cyanobacteria toxin. However, in current literature there is a paucity of reports of human illness caused by exposure to these toxins in aquatic recreational venues. This is not because most recreational lakes are free of blue-green algae. More than 15 Oregon aquatic venues, including heavily used Detroit Lake and Clackamas River, posted cyanobacteria advisories in the last couple of years.
The CDC prints a bi-yearly surveillance report of Water Born Disease Outbreaks across the country. The Dec 2006 issue of MMWR reported that out of nearly 2700 cases of water born illness over a two year period only 22 were due cyanobacteria toxin from two outbreaks in Nebraska. Illnesses were primarily gastroenteritis and skin rashes. There were no reports of chronic neurological illness or death. The next bi-yearly report published in 2008 records more than 4000 cases of water born disease but none were attributed to blue green algae. In these reports fecal bacteria and parasites were responsible for the majority of illness, some of which caused severe illness and even death. Ironically, treated aquatic venues (like swimming pools and water parks) accounted for nearly three quarters of all outbreaks while only about a quarter arose from untreated water venues (lakes & streams.) This raises the question about the cost/benefit of any intervention in Devils Lake that attempts to “treat” the water to decrease risk of injury.
Boating accidents are significantly greater threats to human safety. Page 33 of the 2007 PDF download at US Coast Guard Boating Safety web site reports that boating collisions with other boats, fixed or floating objects accounted for 2030 accidents and 105 deaths country wide that year. Those grim statistics should give pause to a community considering the addition of 20 floating objects to a bustling lake when public safety is our stated concern.
In Summary, my research was unable to turn up sufficient numbers of documented cases of cyanobacteria toxicity to justify the fear that has resulted from all its notoriety. Whereas, fecal bacteria, parasites, and boating collisions with other boats, fixed or floating objects loom as frequent causes of human suffering and death. Is it possible that, given public fear over “bad water,” cyanobacteria advisories alone are adequate to prevent illness? That fix would be both inexpensive and harmless and would leave valuable resources to counter proven threats to the safety of lake users.
Karl Ordelheide MD
Lincoln City, OR