A booming bloom

• Algae bloom

Dan Livdahl, administrator of the Okabena-Ocheda Watershed District stands along a quiet Centennial Beach Monday afternoon in Worthington. Blue-green algae have collected all along the shoreline in one of the worst algae blooms Livdahl has seen on the lake.
• No dumping!

Dan Livdahl illustrates why people should keep their grass clippings, soil and refuse from getting into the city’s storm sewer drains. The items are carried into Lake Okabena and result in the algae blooms now seen on the lake.

Talk about it

WORTHINGTON — It is actually quite pretty until you realize the blue-green coloring that covers the silky sand at Centennial Beach and clings to the rocks along the shoreline is actually decaying algae. With anticipated 80-degree temperatures later this week, it can only mean one thing — the potent smell that comes from algae death is sure to keep even the curious dog out of Lake Okabena for a little while.

A visit to the beach Monday afternoon was void of little children building sand castles and pre-teens floating on inflatable rafts. The blue-green slime coating the eastern and northern two-thirds of the lake is keeping people at bay. Even fishermen had to pull slime from their fishing lines and lures Sunday afternoon.

Dan Livdahl, administrator of the Okabena-Ocheda Watershed District, said this is one of the most wide-spread algae blooms on Lake Okabena he has ever seen. The blooms also started early this year, with the first one discovered in late May near Ehlers Park.

“That is a month or two months earlier than you see the first algae bloom (typically),” Livdahl said.

When another algae bloom occurred during the July 4 weekend along the south shore of Lake Okabena, he received a phone call. Algae blooms in that area are rare because of wind direction.

As for the latest algae bloom, it’s hard to find an area on the lake that isn’t tinted with the blue-green coloring. While Livdahl said skin contact with the algae blooms isn’t dangerous, the blooms can become toxic as they rot.

“You want to make sure that you keep animals out of the water, keep young children out of the water and probably stay out of the water yourself (when it is blue),” he added.

Clarity, excess nutrients to blame

Livdahl isn’t sure why the algae blooms on Lake Okabena are worse this year, though it may correlate somewhat to the lake’s water clarity.

When a Clean Water Partnership study was conducted on the lake in the early 1990s, consultants warned that as sediment is removed from the lake it would allow more light to filter into the water and therefore boost the potential for algae growth.

“For some reason, this year the water clarity has been pretty good,” he said. “There’s a lot of light getting into the water and the sunlight is causing additional algae.”

Also getting into the water are the excess nutrients that fuel an algae bloom, particularly phosphorus.

Grass clippings and organic matter contain high levels of the nutrient. When they get in the street and the storm sewers, they end up in Lake Okabena.

“You don’t need to live by the lake to pollute the lake,” said Livdahl.

He said grass clippings must be kept out of the street and can easily be done by mowing clippings toward the lawn when working along street curbs, sidewalks and driveways.

Any clippings that end up on paved surfaces should be swept up or back onto the lawn.

In addition to grass clippings, soil, leaves and even the soap used to wash vehicles eventually ends up in the lake and contributes to the algae blooms. Fertilizers containing phosphorus also are to blame.

While Livdahl said most of the fertilizers sold in Worthington are phosphorus-free, people can still get access to those containing the nutrient. Unless a landowner takes a soil sample that proves a need for phosphorus, or is establishing a new lawn, he said there’s no need to use fertilizer containing phosphorus.

“Please stay away from phosphorus fertilizer unless you need it,” he said, adding that if it is to be used, it should be applied in the spring and only at the recommended rate.

While nutrients flowing off urban land are typically higher in concentration than the amount of nutrients that come from agricultural land, there are considerably more acres of rural land in the watershed district, said Livdahl.

“We still have runoff that comes off agricultural land,” he added. “More acres means more pollution coming into the lake from agricultural land.”

Lake may be added to impaired waters list

Every two years, Minnesota compiles a list of impaired waters as required by the Environmental Protection Agency. Livdahl expects that Lake Okabena will be added to the list in 2010, along with both Lake Ocheda and Lake Bella, located south of Worthington.

“It’s pretty clear that Lake Okabena fits the impaired water standards,” said Livdahl, adding that all three lakes would make the list because of high levels of nutrients in the lake.

When a lake is placed on the impaired waters list, the typical process is to conduct a Total Maximum Daily Load (TMDL) study. Information is gathered on where the pollution is coming from, maximum daily load levels are set for both rural and urban land, and a prescription for meeting the goals is compiled.

When the lake gets listed on the impaired waters list it opens the doors for funding to aid in addressing the pollution. With the passage of the Clean Water Legacy Act in 2008, additional tax dollars are being set aside to help fund projects such as lake cleanup.

“I’m not sure how that will impact the schedule for TMDL studies or when money to fix Lake Okabena will be available,” said Livdahl, adding that it’s been difficult to convince the state that southwest Minnesota lakes should be a priority.

“Money is now being largely spent in the Lake Pepin and Minnesota River watersheds,” he said. “They’re (also) looking at cleaning the lakes that are easier to fix than the prairie lakes of southwest Minnesota.”

No quick fix

Livdahl said he often is questioned about steps that can be taken to reduce or eliminate algae blooms on Lake Okabena, but unfortunately there is no magic bullet.

“We can do things, but none are without risks to the lake’s ecology,” he said. “Our emphasis in the watershed district and in the city is to do things in the watershed rather than in the lake.”

In recent years, the watershed district has created a sediment dam north of Prairie View Golf Links and established filter strips throughout the watershed to reduce the amount of nutrients that get into the lake.

Less appealing options for the watershed district would be to use copper sulfate in the lake to kill the aquatic organisms, including algae.

Livdahl said such a treatment would require about 14,000 pounds of copper sulfate to be diluted and poured into the lake multiple times during the course of a summer.

“It has some effects that are harmful to the lake in the future,” Livdahl cautioned.

Another alternative would be to use alum, which creates a seal over the sediments on the lake’s bottom and keeps the phosphorus in place. Livdahl said the process works best in deep lakes, but is less proven in shallow prairie lakes because wind action can break the seal.

Pointing to one study on alum’s effectiveness, Livdahl said six of the nine lakes had some water quality improvements. The treatment lasts about 10 to 15 years, but comes at a steep price tag — more than $300,000 for Lake Okabena — and it may not work.

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