“From June 2004 to September 2007, the beach at the lake was closed for 36 weeks, making it one of the most impacted public lakes in the state for blue-green algae toxins,” said Paul Brakhage, water quality expert at NDEQ.

Because of these frequent closings of this one lake in the chain of Fremont State Lakes, the entire state recreation area lost thousands of public visits each summer.

Uncontrolled algae growth can clog these sandpit lakes with bluish-green scum, contribute to fish kills and make them unsafe, foul smelling and unusable for swimming, boating, fishing and water skiing.

It has long been known that nontoxic aluminum sulfate bonds with phosphorus, which is the primary food, source for toxic algae in sandpit lakes, and takes it to the bottom of the lake. Alum, as it is known, forms a flock-like barrier on the bottom of a lake that binds with the phosphorus and keeps it out of the water column. UNL researchers have successfully treated other Fremont State Lakes with the solution in the 1990’s. What hadn’t been tried before was treating one of the lakes after the algae toxins were already known to be in it, as was the case when they treated lake #20 in 2007.

“Water chemistry, the shape and size of the lake and sources of nutrients for the algae to feed on are all factors in how successful treating with alum might be. Typically a treatment can last five to 10 years or longer,” Barrow said.

Several months later the lake was treated with an algaecide, which did not harm the fish, to reduce the amount of algae in the water and make the alum treatment more effective, Brakhage said.

Following treatment, lake water quality results have shown phosphorus is down 85 percent and a result of that is that chlorophyll-a, algae’s biomass, has been reduced 92 percent, resulting in no algal toxins being detected in the lake last year.