Decaying algae odor in the air
WORTHINGTON -- Here comes that odor again -- the acrid, pungent smell akin to rotten eggs. It's hanging in the air just down the shore from Sailboard Beach, but if conditions are ripe -- perhaps with the high temperature and lack of wind forecast for this weekend -- people will likely smell the effects of decaying blue-green algae all around the lake.
Algal blooms happen every year, not just on Lake Okabena, but on lakes throughout southern Minnesota, northern Iowa and across the country. Typically in this region, the blooms (clustered mats of decaying algae) occur in August and September. However, many people may remember the Fourth of July bloom on Lake Okabena last year that kept swimmers and recreationists out of the water for much of the summer.
While there is always the hope the local lake won't experience a summertime algal bloom, a visit to the lake Friday morning showed an abundance of floating, green-colored specks on and just below the surface. Warm, stagnant water typically fuels an algal bloom, but other factors work into it as well.
Okabena-Ocheda Watershed District Administrator Dan Livdahl has been monitoring the waters of Lake Okabena, Lake Ocheda and Lake Bella for more than 20 years. Just in the last week, he's taken water clarity measurements with a Secchi disk ranging from 6 inches on Lake Ocheda to more than 4 feet on Lake Okabena.
Normally at this time of year, the Worthington lake will produce a clarity reading of 2.5 feet. Livdahl said the extra two feet of water clarity this year is likely due to less dirt floating in the water and blocking sunlight.
"A lot of sunlight can lead to more algae," he explained. "That was the warning we got 20 years ago from the Clean Water Partnership -- if water clarity improved, you'd have the potential for increased algae blooms. Clearer water is certainly good news, but there is a potential downside to it too."
The Minnesota Pollution Control Agency released a word of caution earlier this month about algal blooms on lakes across the state. While most algal blooms are harmless, high concentrations of blue-green algae can produce toxins that may be harmful to people, livestock and pets.
"You don't have to be an expert to recognize water that might have a harmful algae bloom," said Steve Heiskary, an MPCA lakes expert. "If it looks bad and smells bad, it's probably best not to take chances with it."
Exposure to a toxic algal bloom can range from irritation of skin, eyes and nasal passages to nausea and vomiting. An animal that has ingested toxins from a bloom can experience vomiting, severe disorders of the circulatory, nervous and digestive systems, and severe skin lesions. In some cases, pets may suffer convulsions and die.
Search for solutions
Livdahl and members of the local watershed board have considered a variety of different options to improve the lake's health and reduce the presence of toxic algal blooms. At its board meeting earlier this month, members discussed the use of Solar Bee technology now being tested on Lake Mitchell in Mitchell, S.D. The Solar Bee is "essentially a big pump that circulates water," said Livdahl.
The pumps can keep water circulating in an area of up to 35 acres, thereby preventing water from becoming stagnant and leading to toxic blue-green algal blooms. Lake Mitchell's pump was installed earlier this spring, and there's no report yet on how successful it has been. Lakes in Oregon and Washington are also experimenting with the technology.
Livdahl said for the Solar Bee to be effective on Lake Okabena, they would need to install 17 units -- at a cost of $45,000 each.
"The units are rather large and would create some big obstacles, which will get in the way of recreation," he added. "They seem to work well in an isolated bay, but we've got one big basin in Lake Okabena."
Another recent discussion among watershed board members has focused on diverting water away from Lake Okabena. In a report commissioned by the Lake Okabena Improvement Association (LOIA), the Wenck Associates engineering firm suggested water flowing into the lake from Whiskey Ditch be redirected to the Heron Lake Watershed District.
Livdahl said HLWD's system is already overloaded, and redirecting the water would not be practical.
Instead, his board is looking at other alternatives. One board member suggested drawing down Sunset Bay and redirecting its waters south through Tripp Slough and into Lake Ocheda, but Livdahl said that's not practical, either.
"The watershed board and people on the lake are investigating possibilities as they come up," he added.
Making an impact
As the watershed and LOIA continue to seek solutions to the recurring algal blooms on Lake Okabena, local residents can do their part to reduce nutrients and sediment that can get into the lake.
One of the easiest steps is to keep street gutters and storm sewer grates free of organic material like grasses, leaves and dirt.
"We're spending more time with construction site erosion control -- trying to keep sediment out of the lake," said Livdahl. "The city is also engaged in efforts to educate citizens to not wash cars (where soap can drain into the storm sewer system) and keep lawn waste out of the gutters."
Those educational efforts, and public response, may have led to added water clarity being recorded on Lake Okabena this summer. Then again, Livdahl said there has also been the absence of large rain events that typically bring a lot of sediment into the lakes.