Zinc Keeps Algae Blooms Out Of Lake But Mining Waste Will Still Be Cleaned Up, Officials Say

The zinc in Lake Coeur d’Alene is helping to keep it free of ugly algae, according to research summarized here Wednesday.

Zinc, which in high enough amounts is harmful to humans, exceeds federal levels for plant and animal life in the lake.

Phosphorus feeds plants. Algae is a floating plant. At high enough levels, zinc dissolved in the water can starve algae by making it hard for the plants’ cells to absorb phosphorus.

Because of federal law, the scientists’ findings won’t slow down efforts to clean up zinc and other mining wastes in the Coeur d’Alene River basin, according to a state environmental official.

Nor should it be an excuse for people to avoid “commonsense” steps to keep phosphorus out of the lake, Geoff Harvey added.

Some of those steps, which include stricter rules on lakeside development, are controversial. They’re called for in a nutrient management plan that is being written primarily to keep algae out of the beautiful lake.

“If people are looking at this (zinc effect) as a safety valve, it’s a safety valve that’s being taken away” by federal laws requiring cleanup of both phosphorus and metals, Harvey said.

There’s more than enough zinc in the lake to keep algae from thriving, according to the research conducted by the U.S. Geological Survey. Scientist Paul Woods, who summarized the findings, said they apply to the lake only north of Conklin Point.

That’s most of the lake, the part fed by the Coeur d’Alene River, which is contaminated by 100 years of mining.

The shallow, southern lake is fed by the St. Joe River. It is low in zinc, and thick with weeds.

If zinc levels remain the same, Woods said, it’s unlikely that enough phosphorus would ever get into the northern lake to cause algae blooms. But there’s been no research yet to determine how much zinc must decrease in order for algae to thrive.

There’s also no evidence that zinc is otherwise hurting the lake. Although there is little life on the tainted lake bottom, there are enough nutrients in the water to feed insects, which in turn feed kokanee salmon and other big fish.

Upstream, however, heavy metals, including zinc, are clearly hurting insect and fish populations - and in some places, threatening human health. That’s why cleanup efforts have begun in Silver Valley streams.

“At the rate we’re poking away at the zinc-loading problem in the upper basin, we probably don’t have to worry about releasing algae in the lake for awhile,” said Ed Javorka, involved in cleanup for the Coeur d’Alene Tribe.

Mining industry spokeswoman Holly Houston said: “It’s nice to hear something good said about zinc besides that it’s a vitamin supplement.”

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