[USA] Although it happens every summer, the blue-green colored waters of Lake Okabena today are a sign that algae continues to thrive in the prairie lake.
Earlier this week, a kaleidoscope of colors ranging from white to a turquoise blue may have looked pretty, but the floating mats of algae signaled danger for people walking dogs eager to cool off in the lake, or for children who might have wanted to take a swim.
Okabena-Ocheda Watershed District Administrator Dan Livdahl said Labor Day weekend is generally when Lake Okabena experiences a severe algal bloom.
“The algae blooms throughout the summer have been normal,” Livdahl said, adding that there were some brief blooms on calm, sunny days in July and August.
“Ehlers Park and Sailboard Beach are normally where the algae ends up being,” he said. “On Saturday, an algae bloom from last week ended up blowing toward the west shore.”
People should be cautious when blue-green algae is present in the lake. The bacteria can be deadly if ingested by dogs, and can cause skin, eye or nasal irritation if people swim in algae-laden waters.
“If you see green paint-like scum near the shoreline, keep your animals out of the lake for sure,” said Livdahl. “It’s not very pleasant to swim in it — it’s smelly. You certainly don’t want to swallow the water.”
Again this year, the city of Worthington has placed a floating boom under the pedestrian bridge crossing Whiskey Ditch at the inlet to Lake Okabena to help keep the algae from floating further up the ditch. In the past, the algae built up in the ditch along Park Avenue, causing a potent smell for neighbors when the bacteria decayed.
Livdahl said putting the boom closer to the lake prevents the decaying algae from settling in the ditch. Any wind and wave action can then break up the floating mats and carry the algae back into the lake.
Despite the presence of suspended algae in the lake, Livdahl said he was surprised that recent water quality sampling he’s done on Lake Okabena shows water quality “seemed to be pretty clear.”
Be resolute, don’t pollute
While people may think they can’t do anything to stop the algae blooms from rising to the surface each summer on Lake Okabena, Livdahl says otherwise.
One of the easiest things people can do is to keep grass clippings from entering city storm sewers. That means that after you mow, go along the curb and sweep up the clippings. If you don’t, the next rain event will carry them to the storm drain and then into the lake, where they become the nutrients that fuel algae growth.
“It’s really easy for people to say, ‘My little bit won’t hurt,’” Livdahl said. “The fact is that adding a little bit of grass to the street eventually adds up. Cumulatively, it becomes a significant source of nutrients.”
In addition to grass clippings, another major source of nutrient pollution is soil. With construction sites and city street work ongoing this summer, contractors should be protecting the storm drains so material doesn’t get into the system.
“(Construction sites) lead to significant nutrients and sediment — if those sites aren’t well managed,” Livdahl said.
Although less of a concern in recent years due to the city’s watering ban, Livdahl said washing vehicles in the street or in the driveway can also contribute to the lake’s algae blooms. Soaps used to wash vehicles, along with dirt that may be carried into the street during the car washing process, contributes to excess nutrients reaching the lake.
Other tips Livdahl offered residents to help reduce pollution are to capture water draining from impervious surfaces by using rain barrels or through creation of rain gardens.
“As you add hard surface to your yard, the more runoff you have going toward the streets,” he explained. “That water is never clean — it always carries some pollution with it.”
The Okabena-Ocheda Watershed District, along with the Heron Lake Watershed District, offer some cost-share if homeowners are interested in creating a rain garden.
Livdahl said that while homeowners can do their part, the city has stepped up as well.
“The city does a wonderful job of street cleaning,” he said. “Most cities clean the streets once or twice a year. Worthington goes out and cleans every street in town multiple times a year.
“That said, we could probably improve water quality if people were keeping the area in front of their house clear of leaves, sticks, grass, garbage and soil.”
View original article at: Lake Okabena’s green… again: Local residents contribute to harmful algae