By Forrest Adams

Dead fish floating in water that looks like green pea soup and stinks like a swamp might tell the story of a blue-green algae contamination. Mitchell Lake in Eden Prairie is contaminated, and the Riley Purgatory Bluff Creek Watershed District is taking actions this summer to begin correcting it.

Two floating, stainless steel, solar-powered water circulation machines, called Solar Bees, were installed in Mitchell Lake last Wednesday as part of a pilot study to treat the harmful algae. The study has wide implications because watershed officials will base the results of this study on the solutions they offer for other area lakes with blue-green algae problems, including Lotus Lake, Riley Lake and Lake Susan in Chanhassen and Round Lake in Eden Prairie.

Watch a video of the Solar Bee installation.

“Most of the lakes have problems with harmful algae blooms,” said David Austin from CH2M Hill, the engineering company that’s heading up this effort for the watershed district. “The blooms happen in mid-to-late summer. Lake Susan definitely has a harmful algae bloom problem. By contrast, Lake Ann (Chanhassen) is in great shape. It’s a real gem … I believe there are also blue-green algae in Riley. It’s probable. Looking at the data, I see that the water clarity gets poor in Riley in late summer.”

The two devices were installed in a southwest bay of Mitchell that’s relatively isolated from the rest of the lake. Austin said the isolation will allow for “some good science.”

Throughout the summer, officials intend to build a “fluid, dynamic model” that they will use to measure the SolarBee effect on the lake water. C2HM Hill intends to conduct a full engineering study on the mixing effects of SolarBee units, testing lake water quality each week in five different locations. Austin said the purpose of this would be to determine how many SolarBee circulators will be needed in the future as watershed officials try to improve water clarity.

“There’s a lot that goes into improving water clarity,” he said. “We want to eliminate the nuisance of blue-green algae. All by itself, it’s a good thing. At the same time, once we get there, it also opens the door to some other techniques we can use to improve water quality, such as the stocking of predatory fish or bio-manipulation techniques.”

The decision to rent or purchase the units would be made in the middle of the winter. He guessed next year there could be four or five units installed in Mitchell. The watershed district could apply the rental fee of $12,000 each toward the purchase of these and additional machines ($45,000/unit) if they are found to be effective. The machines, on loan from SolarBee Inc., of Dickinson, N.D., are scheduled to be removed in September.

At a time when everybody is faced with dramatically higher costs as a result of high fuel prices, the solar-powered models are quite attractive, said Austin. Austin referred to it as “the most sustainable, low-energy solution.” They circulate 10,000 gallons of water per minute. Using a propeller, in the center of an underwater gradual sloping cone shape, it creates a 4- to 6-foot diameter column of rising water below the machine that spreads upward and outward across the top of the lake. One machine can affect up to 45 surface acres. The upper waters of the lake, where blue-green algae (cyanobacteria) grow, are put into a slow, but continuous, motion. Meanwhile, three 80-watt solar panels provide the machine with enough energy to run a sealed, magnetic motor and digital control box virtually all day and night. The digital control adjusts to the weather, slowing down at night and during times of sustained cloudy weather to conserve power. Even in clouds, the solar panels absorb the sun’s UV rays.

Austin explained that blue-green algae float to the surface, hence the need to circulate water and push them down, while green, non-toxic algae that are beneficial to the lake’s ecosystem sink. He said it’s detrimental to the lake.

“When [blue-green algae] accumulate on the surface, it’s like drawing the shades on the lake. Other things don’t get enough light to survive,” Austin said. “It’s important that we suppress the blue-green algae.”

Blue-green algae thrive in warm, shallow, nutrient-rich lakes, and are commonly found in central and southern Minnesota, according to the Minnesota Pollution Control Agency.

“Not all blue-green algae blooms are toxic; in fact, the vast majority of them are not,” says the MPCA Web site. “But because they can occur so quickly and can vary so much in toxicity and frequency, all blue-green algae blooms are potentially dangerous. They cannot be accurately predicted and there are no easy laboratory tests for the toxins produced. A blue-green algae bloom can change from non-toxic to toxic or vice-versa without a significant change in appearance.”

Excessive nutrients in the lake, lots of sunlight and warm temperatures all encourage the growth of blue-green algae. They are problematic when there’s a “bloom.” At this time, they can produce the toxins. For people, health problems that might result from exposure to blue-green algae include irritation of skin, eyes and nasal passages, and nausea and vomiting. Extreme cases can produce paralysis and respiratory failure.

SolarBee Inc (SI) develops and manufactures machines that use solar power instead of grid power, and they reduce or entirely eliminate the need to add chemicals to treat a body of water, according to the Web site. SI invented solar-powered long-distance reservoir circulators in 1998 and named this technology “SolarBee” in 2001. In 2002, the high flow (40,000 lpm/10,000 gpm) machines were developed that allowed the technology to be expanded from small wastewater ponds to large lakes. In 2004, the large heavy-duty brushless motor was developed with a battery system for day-and-night operation. In 2005 and 2006, a digital controller was developed with an on-board GPS receiver, data logging, flash-card programming to fine tune the performance for each reservoir, LED diagnostics, and a SCADA radio-link output for remote machine monitoring. High wave machines were also developed to withstand harsh conditions in extremely large reservoirs. By 2008, more than 1,400 SolarBee circulators had been successfully deployed in hundreds of water bodies to improve water quality without reliance on grid power or chemicals. In 2004 the company won a state-wide Industrial Development Award in North Dakota and in 2006 an Environmental Award in both New Mexico and Australia. In 2008 the North Dakota Entrepreneur of the Year Award was presented to its founders, Joel Bleth and Willard Tormaschy. Readers can contact Forrest Adams at fadams@swpub.com.