Aquatic Weed & Algae Treatment Program

Out-of-Control Vegetation in Geist Reservoir

Many Geist residents are wondering how the excessive invasive weed growth within Geist can be controlled. You may have thought about the possibility of using chemicals, either aquatic herbicides or algicides, to control the weeds. But first there are some questions worth addressing: Do you know whether the use of chemicals in this body of water will be safe for you and for the environment? Are you using approved chemicals? Have you obtained a permit?

Although the weeds are invasive and annoying, the ideal situation is to maintain some native species of vegetation to provide habitat, shelter, and oxygen for fish and other organisms, plus positively provide nutrient competition for the blue green algae. After all, these plants provide the base of the aquatic food chain. What’s more, the larger plants in a body of water also stabilize the sediments that would otherwise be erodible. Unfortunately, there are situations in which invasive species of aquatic plants, such as Eurasian milfoil, can gain a foothold in a body of water. These plants continue to grow and form a canopy over the surface of the water. This canopy of vegetation will eventually extend, shade out, and kill the native species that are growing below it. Ultimately the Eurasian milfoil can take over a body of water up to 10 feet deep, making it challenging to swim or fish or conduct just about any other recreational activity. Removing heavy sediment and nutrient loads that are exacerbating the situation by literally feeding the problem is also of concern. Dredging in key areas of the reservoir is currently under engineering study, and in partnership with key stakeholders a dredging project is likely in the near future.

Dealing with Eurasian milfoil

If you insist on removing the milfoil manually, you should pull up by the roots, keeping the plant intact as you dispose of it. The idea is to avoid breaking off pieces that can float off and reseed elsewhere. Excessive weed control and improper use of herbicides can destroy valuable habitat by releasing nutrients into the water, which in turn can stimulate the growth of algal blooms (rapid accumulation of microscopic algae). These algal blooms will cause water to turn an unsightly green. Once they die off or “crash,” they can deplete the water of oxygen and cause a subsequent fish kill. Worse yet is when algal blooms become toxic, posing a threat to our health.

Algae can be controlled using copper compounds, particularly copper sulfate, which is probably the most widely used of the algicides or herbicides in bodies of water. Herbicides must be used wisely in the environment to prevent adverse effects to the organisms that live in it.

Typically Citizens Water will treat with an algicide to avoid foul taste and smell in our water supply as a result of high algae growth. However, it doesn’t normally treat for the invasive Eurasian milfoil. If you are unsure about the safety and impact of a particular product, you should visit to learn more.

Geist Lake Coalition Kicks Off Pilot Program to Reduce Eurasian milfoil

The best remedy for algal blooms is a worthy watershed management program. Fortunately, the Geist Lake Coalition along with the Geist/Fall Creek Watershed Management have invested heavily in a watershed management plan.

We are currently studying and implementing programs that were a result of this study, and we need your help as we get these programs off the ground. Whether it’s time, talent or treasure, we need your help!

Invasive species such as Eurasian milfoil should be controlled when new patches of growth appear in the water. Established infestations should also be managed in order to prevent the invasive species from taking over vast areas of the reservoir. This is where the Geist Lake Coalition has focused its efforts, and where residents and homeowner associations have turned their attention. The correct and approved herbicides can be used selectively to remove Eurasian milfoil from stands of native aquatic plant species, leaving the native species to function in their normal roles as producers of habitat, shelter, and oxygen.

The Geist Lake Coalition has applied for and successfully received an L.A.R.E. (Lake and River Enhancement, as administered by the DNR) grant for a pilot program to treat Eurasian milfoil on Geist. By no means are there funds currently available to continue treatment beyond the pilot program’s current scope.

We need your help to fund our matching portion of the grant and beyond what the grant will fund. The more funds underwritten by local businesses, homeowners and homeowner associations, the more areas we can treat within the reservoir. The contributions you have consistently made toward our fireworks display have mostly funded our programs to date, but with the major effort of late we have quickly outstripped those funds! Whether it’s financial support for our annual 4th of July celebration or water quality, it’s the same set of pockets. Please consider a tax-deductible donation (we are a 501c3) to the Geist Lake Coalition.

Thank you in advance for your serious consideration to become a stakeholder in this effort and for your generous support.

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