Chemical Treatments: A Short-Term Fix That Makes Things Worse
Many lake managers turn to algaecides and herbicides to control harmful algae. On the surface, these treatments may look effective, but the reality is very different.

When algae are killed by chemicals, the cells release toxins directly into the water. The dead material then sinks, decomposes, and consumes oxygen—creating hypoxic conditions that stress or kill fish. Low oxygen also triggers internal nutrient release from sediments, fueling the very blooms that the chemicals were meant to stop.

Instead of restoring balance, chemical treatments can lock lakes into a cycle of recurring blooms and declining water quality.

Looking at the Surface Isn’t Enough
It’s common to judge a lake’s health by what can be seen at the surface—clear water, healthy oxygen levels near the top, or visible fish. But many lakes stratify, with deeper waters cut off from oxygen. While the surface looks fine, the bottom layers can be oxygen-depleted and nutrient-rich.

Fish crowded near the surface aren’t thriving—they’re escaping conditions that are deadly below.

Runoff Isn’t the Only Problem
Nutrient runoff from land is an important driver of algae, but it’s not the only one. Sediments at the bottom of lakes often act as storage banks for phosphorus and nitrogen. When oxygen levels drop, these nutrients are released back into the water, feeding new blooms year after year.

Focusing only on reducing runoff misses the internal nutrient cycle already at work inside the lake.

The Limits of Simple Metrics
Common tools like the Trophic State Index (TSI) are often used to measure lake health. But they mostly track surface-level data like clarity and nutrient concentrations. These numbers don’t reveal what’s happening in deeper waters, or how sediments and oxygen loss are driving long-term decline.

A Call for Smarter Lake Management
The misconceptions around lake health—and the overreliance on chemicals—are keeping many lakes stuck in poor condition. Chemical treatments may offer short-term relief, but they create long-term problems.

To break the cycle, management strategies need to focus on oxygen restoration, sediment nutrient control, and ecosystem balance. Prevention and smarter monitoring are also key to creating lakes that are resilient, healthy, and able to support aquatic life for generations.

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Environmentally Friendly New Years Resolutions

Lake Erie Faces Collapse

Blue Green Algae

Wisconsin Wetlands Association Conference

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Zebra mussels can filter out the Microcystis with other particles, but then they spit out the Microcystis because evidently it is unpalatable to them. The researchers suspected the zebra mussels were consuming competitors of Microcystis, which paved the way for the cyanobacteria to flourish under lower nutrient availability than it usually needs.

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Des Moines Water Works, after dumping as much as $250,000 a year into buying water from the increasingly polluted Saylorville Lake, is now considering a $50 million treatment plant expansion. But who will pay for it?

The report that labeled the Raccoon River endangered blamed the problem on the farm chemicals and livestock manure that are running from those emerald fields into our increasingly sickly green rivers and streams. However a lawsuit to share the cost with upstream polluters failed along with a separate case against the state of Iowa alleging the state was violating the public trust by failing to protect the Raccoon River from pollution.

Read More https://iowacapitaldispatch.com/2021/07/12/green-water-is-costing-iowans-millions-of-greenbacks/

This year, a different approach was taken. Starting in June, contractors sprayed the lake with a compound called Phoslock, which helps remove phosphorous from the water. Then an aquatic vegetation harvester trawled across the south end of the lake, chopping down underwater weeds and hauling them to shore. The goal – to remove as much phosphorous from the lake as possible.

Sediment in the lake – from decomposing weeds, lawn fertilizer, stormwater runoff – produces excess phosphorous, which acts as fuel for algae blooms. Relatively few outflow points on the lake result in a slow turnover rate of water and poor nutrient cycling, according to a 2011 Kitsap Public Health District report.

The harvester removes plant life and opens the water up to circulation, allowing for the water to mix and more sunlight to reach the deepest parts of the lake

There are other ways to remove invasive plant species that may not require chemical spraying. James Douglass, an environmental scientist at Florida Gulf Coast University says the other methods could have several benefits and chemical spraying is actually the worst way to solve the problem.

Douglass agrees that other methods create a win-win for everyone. “It takes that rotting material out of the water and actually uses some of the materials from those aquatic weeds as fertilizer and return nutrients to the land where they’re needed instead of having them cause algae blooms in the water,” he said. An aquatic weed harvester not only opens waterways for navigation, but it is very effective in removing excess plant material.

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The Friends of Georgica Pond Foundation, a group of pondfront property owners, know that removing the plant material is particularly helpful in lowering phosphorous levels in the pond. By doing so, “harmful algal blooms and ecological crisis” can be prevented. There is a definite correlation between operation of the weed harvester and improved water quality.

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Georgica Pond has been invaded by toxic cyanobacteria, or blue-green algae, in recent years, which can cause serious health problems.  For the second consecutive year, the foundation has leased an aquatic weed harvester to remove plant material, or macroalgae, from the pond, which releases nitrogen and phosphorous as it decays and is believed to promote cyanobacteria.

The mechanical harvester 32,700 pounds of this material represent 6% of the pond’s nitrogen load and 12% of its phosphorous load; down from 2016 when 55,740 pounds, representing 13% of the nitrogen load and 23% of the phosphorous load, were harvested.  Officials say part of the reason for the decrease in 2017 was due to the large quantity of macroalgae harvester the previous year.

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Some blue-green algae produce toxins that could pose a health risk to people and animals when they are exposed to them in large quantities.  Health effects could occur when ingested, inhaled, or through contact with the skin.  Ingestion of the algae affects the liver and the nervous systems and even causes death in livestock and pets when large amounts have been consumed.  Vomiting, diarrhea, asthma, headache, fever, and muscle weakness are also potential health effects of the blue-green algae toxins.

Blooms of blue-green algae that last more than a few months can be harmful to lake/river ecosystems and cause fish kills because of the decrease in oxygen levels and direct ingestion in the food chain. Blue-green algae blooms block sunlight that feeds plants growing on the bottom of lakes, resulting in the loss of rooted aquatic vegetation, which is valuable fish habitat.

Algae use sunlight to make food and are eaten by microscopic animals (zooplankton). Small fish eat the zooplankton, and larger fish and other large animals eat the small fish. However, blue-green algae are often difficult to eat or are of poor nutritional value for zooplankton. Consequently, zooplankton, particularly types that are the best fish food, often decline during blooms. This decline can impact the number of desirable game fish.