Chemical treatments of Half Moon Lake have made the water clearer in the past 10 years, but the city is looking at more permanent measures to keep the recreational waterway from becoming murky again.

Getting at the root causes of why the lake sometimes has algae blooms and outbreaks of aquatic weeds is the aim of a new plan, which could help the city get grant money for some long-term fixes.

“As early as 2020 it would open grant opportunities for the city,” city engineer David Solberg said.

The plan is going through some revisions, but will be on its way to the Environmental Protection Agency for approval by the end of the year. While the document itself doesn’t assure grant funds, having a plan like it is a requirement or improves chances for a city seeking funding from different state and federal water quality programs.

Putting permanent measures in place would also greatly reduce the need for chemical treatments of the lake that have been happening since 2009.

“That would be our end goal, that we wouldn’t have to do that,” said the city’s community services director, Jeff Pippenger.

The city has been using annual applications of Aquathol, a herbicide, to curb growth of curly-leaf pondweed — an invasive aquatic plant that can crowd out native species in the lake. About every other year, the city has also applied alum — a chemical harmless to people and wildlife — to bond with excess phosphorous in the lake, tying up the nutrient so it can’t feed algae blooms.

State Department of Natural Resources grants have helped pay half or more of the costs of those treatments — picking up 75% of the tab for the $66,120 alum treatment slated for this year — but the city still pays the rest.

The city’s first alum treatment in 2011 was originally expected to be a long-term fix, sinking to the bottom of the lakebed and bonding with the phosphorous in the soil.

“The alum treatment was supposed to be one-and-done, and that hasn’t been the case,” Pippenger said.

Water clarity gradually declined and the city did another alum treatment in 2017, planning then to make it a biennial defense against algae blooms.

Coming and going

Parts of the new plan would address how fresh water comes in and seeps out of Half Moon Lake.

About a million gallons a day is pumped from the Chippewa River from equipment in Owen Park and piped into Half Moon Lake. Without the influx of water, the old oxbow lake does not have enough of its own spring water to sustain itself and it would dry out. But tagging along with the river water is more phosphorous.

“That’s what’s creating a lot of our phosphorous intake,” Pippenger said.

And not too far from where fresh river water comes into the lake is a way it can then sneak back to where it came from.

“There is a leak in Half Moon Lake,” Pippenger said.

Located on the south end of the lake, just east of the Menomonie Street entrance to Carson Park, Becca’s Brook flows underground from the lake to the Chippewa River.

The Becca’s Brook leak is “more than a theory,” Pippenger said, but still needs more investigation into how much water it lets out of the lake.

The continual departure of water from the lake causes the ongoing need for pumping, which brings more phosphorous to the lake.

But the new plan suggests projects to stop that cycle, such as adding a filtration system to the pumping equipment and finding ways to stop the seepage from Becca’s Brook.

Another problem on the lake mentioned in the plan is occasional closures of Half Moon Beach due to high bacteria levels caused by Canada geese droppings.

The city already has employed various efforts to control the geese population in the area, such as applying cooking oil to eggs so they don’t hatch and roundups every few years when the flock grows too large.

Those strategies have been successful at reducing beach closures, Pippenger said.

“We’re seeing less and less of a problem there too,” he said.

Task force reunion

In addition to submitting the new plan to the EPA, the city also will soon be gathering a group to review almost 18 years of work done to clean up the lake.

“Since then we’ve seen a significant water improvement in Half Moon Lake,” Pippenger said.

The meetings will reunite some who were involved in task force that created a lake water quality plan in 2002, later updating it in 2010.

Efforts enacted since then included the water treatments, prohibiting motorboats on the lake and harvesting aquatic weeds.

Aside from a documented improvement in clarity over the years, the Eurasian milfoil — an invasive aquatic plant — was eradicated from the lake after a 2009 herbicide treatment.

The group will assess how successful past measures have been while also planning what to do in the coming years to improve the lake.

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