LINCOLN, Neb. -- State and University of Nebraska-Lincoln water and wildlife experts may have found a one-two-three punch to knock out toxic algae and restore water quality in Nebraska's numerous sandpit lakes.



"It seems to be working very well so far," said UNL Extension surface water quality specialist Tadd Barrow.



The process to rid the algae-prone Fremont State Lakes of the oily green scum that can close them at the height of the summer recreation season is a combination of ridding a lake of its rough fish population, treating it with an agent that takes the algae's primary food source out of the water and then restocking it with sport fish.



That's the combination that UNL water management specialists, water quality experts from the Nebraska Department of Environmental Quality and fisheries experts at the Nebraska Game and Parks Commission used to get Fremont Lake No. 20 off the list of perennially closed lakes when they killed off its population of carp and other rough fish and treated the lake with aluminum sulfate two years ago.



"The result was the lake wasn't closed at any time during the 2008 recreation season and we think that trend will continue this year," Barrow said. Though numerous Nebraska lakes have been closed due to blue-green algae infestations over the last few years, Fremont Lake No. 20 was a virtual poster child for the problem until the state and UNL experts developed their plan to clean it up long-term.



"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 long has 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 successfully treated other Fremont state lakes with the solution in the 1990s. What hadn't been tried before was treating one of the lakes after the algae toxins already were known to be in it, as was the case when they treated lake No. 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.



To help ensure the treatment would take hold and last, and to begin the process of restoring the lake as a fishery, it was treated with Rotenone, a gill-targeting pesticide that killed the lake's population of mostly carp and white perch which contribute to the phosphorus algae eats.



Two months later, the Game and Parks Commission restocked the lake with bluegill, largemouth bass and channel catfish.



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.



"The difference in the clarity of the water is amazing, as well," Barrow said. "Last spring (2008) you could see the bottom of the lake in 18 feet of water."



Water quality and fisheries monitoring of the lake will continue for several years, but Barrow is confident that the combination of clean-up and treatment options used at Fremont Lake No. 20 will be successful long term and that they could prove applicable for other chronically algae infested sandpit lakes.



"We think the initial success at lake No. 20 will do a lot to get past the stigma that Fremont State Lakes has had over the last few years for being closed due to toxic algae problems. We think this treatment method is applicable elsewhere as well," he said.



Although alum is more expensive to apply than the traditional algae treatment, cooper sulfate, it is nontoxic and lasts far longer. Copper sulfate kills fish and other aquatic organisms along with the algae and does nothing to reduce a lake's nutrients and cooper treatment often has to be repeated several times annually.



The Nebraska Environmental Trust and Nebraska Game and Parks Commission provided funding for treatment of Fremont Lake No. 20. Funding for water quality monitoring was provided by UNL and Clean Water Act Sections 106 and 319 Funds by NDEQ and the U.S. Environmental Protection Agency.



SOURCE: University of Nebraska.