Fish kill at Hancock County lake marks start of algae season

A substantial fish kill last week on north-central Iowa's Crystal Lake may herald the beginning of what's becoming known as the state's algae season.

An intense blue-green algae bloom over the Fourth of July weekend preceded the fish kill, which became apparent Wednesday, according to Department of Natural Resources fisheries biologist Scott Grummer.

The algae's extraordinarily rapid die-off consumed much of the 264-acre lake's available oxygen, killing large numbers of game fish and panfish, Grummer said.

'It's rare to have the algae die off so suddenly. Usually it's more gradual, with time for aquatic plants to replenish the oxygen lost during the algae's decomposition,” he said.

The lake, about seven miles west of Forest City, had been renovated in 2008 and was becoming well known as an excellent fishery, Grummer said.

Grummer said Friday that dissolved oxygen levels remain low, and more fish may yet perish.

Surveys will be conducted later this summer to determine how much supplementary stocking may be necessary, he said.

The blue green algae that caused the fish kill also can produce microcystin toxins that can make people sick and be deadly for dogs, livestock and other animals.

So far this summer, the DNR, which monitors microcystin levels at 39 state park beaches, has posted 14 swimming advisories cautioning Iowans to stay out of the water at 11 beaches because of elevated microcystin levels.

Last summer, the DNR posted 22 beach warnings for high levels of microcystin. Advisories are posted when toxin levels reach 20 micrograms per liter.

One of the two main ingredients for algae growth - waterborne nutrients, primarily phosphorus - is plentiful, as usual, in Iowa waters, said Susan Heathcote, water programs manager for the Iowa Environmental Council.

The second ingredient - summer heat - has been less prevalent than usual, but the hottest weeks of a typical summer lie ahead.

Stuart Schmitz, an environmental toxicologist with the Iowa Department of Public Health, said the DNR issued just two microcystin advisories this week, down from five the previous week.

Schmitz said the Department of Public Health is adding 'microcystin-toxin poisoning” as a permanent addition to the list of ailments that doctors must report to the state.

Iowa has had two reported cases so far this year and typically has about six per year, he said.

Microcystin can cause breathing problems, upset stomach, skin reactions and even liver damage. Inhaling water droplets containing toxic blue-green algae can cause runny eyes and nose, cough, sore throat, chest pain, asthmalike symptoms or allergic reactions.

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