Mattoon Prepares to Maintain Stable Algae Levels

City takes proactive measures after last year's 'do not drink' orders due to algae toxins

Apr. 14, 2026 at 2:49pm

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An extreme close-up X-ray image revealing the intricate internal structure of a water filtration system, with glowing lines and ghostly shapes representing the complex mechanisms designed to remove contaminants from the water.Mattoon's water treatment upgrades aim to remove more of the nutrients that fuel harmful algal blooms in the city's water supply.Mattoon Today

After two separate 'do not drink' orders were issued last year due to neurotoxins from algae growth in Lake Mattoon and Lake Paradise, the city of Mattoon, Illinois is taking steps to prevent a repeat this year. This includes applying for an EPA permit to use algaecide treatment, commissioning a study to understand nutrient levels in the lakes, and upgrading their water filtration system to remove more of the algae-feeding substances.

Why it matters

Mattoon's water supply issues last year highlighted the growing threat that harmful algal blooms pose to communities, especially as climate change leads to warmer temperatures and increased rainfall that can fuel algae growth. The city's proactive approach aims to safeguard public health and avoid disruptions to the water supply.

The details

Mattoon's Public Works Director David Clark said the city is taking several key measures, including daily water testing, applying algaecide treatment where needed, and upgrading to more advanced granular activated carbon (GAC) filters to remove more nutrients that feed algae growth. The city is also commissioning a study to better understand the nutrient levels in the two lakes that supply its water. Additionally, Mattoon plans to pilot an ozone treatment system starting in May or June.

  • Last July, neurotoxins from algae growth led to 'do not drink' orders in Mattoon.
  • About 4-5 weeks ago, Mattoon applied algaecide treatment to Lake Paradise after testing indicated it was needed.
  • Mattoon is aiming to have the new GAC filtration system installed sometime this year.

The players

David Clark

Public Works Director for the city of Mattoon, Illinois.

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What they’re saying

“Our numbers have been extremely good”

— David Clark, Public Works Director

“Where we did treat Paradise, I think it was, what, about a month ago, 4 or 5 weeks ago, and they have come back in and done a follow up. And the numbers are really good right now”

— David Clark, Public Works Director

“Get more runoff and some of the, you know, the fertilizers and stuff that go on fields and people that put on their yards. I mean, that all eventually gets in the streams and lakes and so forth. And, this blue green algae just loves phosphorus and nitrogen and heat”

— David Clark, Public Works Director

“What they call GAC filters. These are granulated, activated carbon filters rather than just sand filters that we'll put in there. And that'll start taking out more of that stuff too. So that's going to be something we'll probably get done within this year”

— David Clark, Public Works Director

“We're pretty confident, you know, that we're a good handle on. We'll keep a close eye on it”

— David Clark, Public Works Director

What’s next

Mattoon plans to start piloting an ozone treatment system for the city's water supply in May or June.

The takeaway

Mattoon's proactive approach to managing algae levels in its water supply, including applying algaecide, upgrading filtration, and studying nutrient levels, demonstrates how communities are having to adapt to the growing threat of harmful algal blooms driven by climate change and agricultural runoff.