Fish Kill Event - Private Lake

The DNR investigated a fish kill in a seven-acre privately owned lake about two miles north of Riceville Monday.

Several hundred dead fish, ranging in size from two to 18 inches, were visible around the edge of the pond.

DNR specialists found no immediate cause of the fish kill, although dissolved oxygen levels were very low, one part per million (ppm) or less. Levels were low where a small

stream entered the lake and where water left the lake, flowing downstream about one-fourth mile to the Wapsipinicon River. Low oxygen levels can be toxic to fish and other aquatic life.

However, dissolved oxygen levels upstream in the small creek that feeds the pond and in the downstream Wapsipinicon River were normal, well above six ppm, the level of oxygen that fish need to survive.

“This one has us puzzled,” said Cindy Garza, an environmental specialist at the Mason City DNR field office. “Ammonia levels were normal. There was no sign of a pollutant or manure near the pond. And, the algae was not dying off which might cause oxygen levels to drop as the algae decays.

“We did see a slight sheen on the water which might indicate fuel or a petroleum-based product such as some pesticides,” she added.

“That indicates that something happened nearby to cause oxygen levels to drop drastically,” Garza said. “The area has had several inches of rainfall in the last week, which could have washed something into the pond.”

The fish kill was reported by the landowner who noticed it over the weekend.

The DNR is having water samples tested for pesticides, biological oxygen demand and ammonia and expects results back next week.