WORTHINGTON -- While most visitors to Sailboard Beach this weekend will be looking out over the water, they may want to look down as well. Water clarity in the local lake has been the best it has ever been since a testing program was initiated in 1998.
Okabena-Ocheda Watershed District Administrator Dan Livdahl measures water clarity on the lake with a Secchi disk, which is lowered into the water and pulled back up until it comes into view. In his official testing of water clarity on May 23, Livdahl measured a maximum visual depth of 5 feet, 3 inches in the middle of the lake. On Thursday afternoon, it was 2 feet, 4 inches closer to shore.
The average water clarity in May on the lake is less than 2 feet, while the best water clarity measurement taken prior to this year was less than 4 feet, Livdahl said.
"If the wind comes up, water clarity can change fairly fast," he added.
Livdahl attributes the improved water clarity to less phosphorus pollution in the lake.
"I think that comes from the filter strips we have in place, the sedimentation basin we have north of Worthington and the people of Worthington being more conscious about keeping grass clippings out of the gutters," he said. The city also makes more passes with the street sweeper to keep debris from reaching the storm drains; and farmers utilize better land management practices.
Water clarity measurements will continue to be collected on a monthly basis on Lake Okabena, and Livdahl said the Okabena-Ocheda Watershed District is working with a consultant on a monitoring plan that may require twice-monthly water quality testing.
New this year, the OOWD will also take readings of the lake's dissolved oxygen content each week. This test is hoped to provide the district with some answers to the annual summer algal blooms on the lake.
"The question we're hoping to answer is whether dissolved oxygen gets low enough that nutrients are released from the bottom sediment sometime during the season," Livdahl explained. "When dissolved oxygen gets low, the bottom sediment can release phosphorus. We don't know if that's happening or not."
Phosphorus is the food that spurs algal blooms.
"In Lake Okabena, a bad algae bloom is caused by a lot of phosphorous, a lot of nutrients, sunshine and warm temperatures," Livdahl said.
The dissolved oxygen levels will be measured at three of the deeper areas of Lake Okabena --at a 7-foot depth in the center of the lake, an approximately 13-foot depth near Sailboard Beach, and an 11- to 13-foot depth along the western portion of the lake.
"It's most likely that dissolved oxygen would be low in the deeper portions of the lake," Livdahl said, adding that these deeper portions are slowly filling in with sediment.
Whiskey Ditch treatment
Following a decision earlier this year to try Bioverse products in response to algal blooms, the watershed district and the E.O. Olson trust will spend up to $4,000 this year to address algae issues in Whiskey Ditch and a storm water pond in the Glenwood Heights addition.
"The original concept was to treat all of Whiskey Ditch, but in rethinking this, we're looking at where the algae is a problem in a normal year," Livdahl said. "The real problem is between the lake and the boom we have installed near the 10th Avenue bridge. That's where algae blows in from the lake, gets stopped by the boom and dies there and rots."
Livdahl said the boom was put in place years ago to keep algae from blowing further up the ditch. With the concentrated levels of algae there, the plan is to add Bioverse products, containing bacteria enzymes, to cause the organic matter to decay at a faster pace. The anticipated result is reduced odor and a shortened duration of it.
"If they can stop the stinking in Centennial Park, they'll be a hero," Livdahl said of the Bioverse product. Bioverse is a local company, located in the Bioscience Advancement Center on Worthington's north side.
Livdahl said if the Bioverse products appear to work this year, it may be used more in the future. There are no safety issues involved with the product.
"They are natural products ... that are present anyway in surface water in this part of the world," he added.
Daily Globe Reporter Julie Buntjer may be reached at 376-7330.