Yucky muck: It takes a village to improve lake health
WORTHINGTON — Since late June, water quality and clarity in Worthington’s Lake Okabena has struggled.
It isn’t uncommon to see blue-green algae blooms push toward the shoreline each summer. On Monday, the dead and decaying bacteria — accompanied by its pungent odor — was carried onto the rocks and sand at Sailboard Beach, beached on the boat landing at Ehlers Park and floated along South Shore Drive.
Summer sunlight, rising water temperatures and an abundance of nutrients fuel the growth of blue-green algae, a bacteria that can contain toxic microcystin algae. Since people can’t tell if it’s toxic by looking at it, it’s best to stay out of the water. Dogs have died from ingesting toxic lake water, and cattle are also at risk if drinking stock pond water containing the toxic algae.
The impact to people exposed to the cyanobacteria may include skin rashes if swimming in algae-laden water to respiratory issues similar to allergic reactions.
Okabena-Ocheda Watershed District Administrator Dan Livdahl is tasked with monitoring water quality and clarity in the local lake. After years of collecting water samples, taking secchi disk readings and watching the algae blooms form, die and disappear, he’s recorded some trends.
In a typical year, Lake Okabena maintains fairly good water clarity in the spring. Usually by the city’s Windsurfing Regatta in early June, however, the lake experiences its first algae bloom, Livdahl said. Most summers, the June bloom is short-lived and lake recreators get a break from the blue-green muck until mid- to late July.
“Then, for the rest of the season, the lake is usually pretty green,” he added.
The warm water becomes the perfect environment for algae, and when it gets too warm, it dies and washes ashore.
“That’s why it smells so bad,” Livdahl said. “The algae really likes calm days or days where there’s not a lot of wind. The top 6 inches of water is where most of the algae grows.”
That’s also where the water is warmest.
Farther out from shore, Livdahl said water clarity is better, though water quality is still reduced by suspended sediment in the water.
It takes three ingredients to stimulate algae growth in a lake — sunlight and warm water (which humans can’t control over) along with nutrients.
“What we can control is the amount of fertilizer in the water,” Livdahl said, noting that phosphorus is the primary fertilizer that leads to algae blooms.
Phosphorus was once a primary ingredient in lawn fertilizers, though manufacturers have worked during the past decade to remove phosphorus from their products. Today, phosphorus is more likely to reach the lake from grass clippings mowed into the streets, as well as leaves.
Both are carried along the curbs of city streets and into storm drains. There, water carries the organic material to either Lake Okabena, Lake Ocheda or Heron Lake, depending on what part of town a person lives.
“Earlier this season, there were a lot of grass clippings in the street,” Livdahl said, asking residents with a mulching or side chute mower to keep the grass clippings on their yard instead of directing them onto sidewalks, driveways and streets. Clippings that end up on the impervious surfaces should be swept back onto the lawn.
Livdahl isn’t the only one asking for the public’s cooperation. According to city ordinance No. 9204, it is unlawful to place “leaves, litter, grass clippings, or brush as to obstruct the free flow of water in a natural waterway or a public street drain, gutter or ditch,” according to Myra Onnen, Worthington’s Community Service Officer.
Onnen said she typically issues a warning to violators, giving them a couple of hours to sweep up the debris before she returns for a follow-up check. She can issue a $90 ticket to those who don’t comply.
Onnen notifies violators when she’s doing her normal patrol, but said people are welcome to report specific properties by calling the Worthington Police Department (295-5400) and asking for the community service officer.
In addition to grass clippings and leaves, Livdahl said black soil also contains organic matter than can pollute the lake.
“When people are doing construction, landscaping or planting trees, they have the potential to get soil into the street gutters,” Livdahl said. “Any of that black soil that gets into the streets will provide material for algae blooms.”
Soap also contains phosphorus, so people who prefer to wash their car at home should avoid doing so on the driveway or in the street, he added.