Why does everyone ask about lake muck? 

Whenever you talk about aquatic plant management, regardless of where you are in the country, you always get a few of the same questions and concerns from stakeholders. One of the most common, whether you are in Florida, Connecticut, or somewhere in between, “Doesn’t spraying aquatic plants just send toxic muck to the bottom of the lake”? This is a great question. So, let’s try to answer this in parts. 

What is muck?

“Muck” is a catch-all term that refers to all the dead organic matter that settles to a lake bottom. This organic matter is a collection of decaying plants, fish, algae, or any other critters that have settled to the bottom. Said another way, muck is natural. It is an unavoidable part of lake aging and, in and of itself, it is not bad. Honestly, a little muck, in the right places, is actually a very good thing since it helps support a wide variety of insect larvae, worms, snails, and other species that are critical to a healthy-lake food chain.  

So, why do people think muck is bad?

Unfortunately, like most parts of life, too much of a good thing can become a bad thing. When muck buildup becomes excessive, it essentially begins to rot on the lake bottom. As bacteria start to consume this organic matter, they also consume all the oxygen. With the oxygen gone, the helpful critters that once lived in the muck must leave. Moreover, the lack of oxygen means the organic matter starts to ferment and this process causes methane and hydrogen sulfide (sewer gas) to form, which further creates an environment that is unhealthy for fish, plants, and other desirable lake creatures.  

Topped-out Hydrilla verticillata in a small pond

What causes muck levels to go from good to bad?

A healthy lake is a diverse lake. It has a wide variety of native plants, fish of various types and sizes, and a well-established food chain to support all these organisms’ needs. In this scenario, the diversity of life helps keep everything in check. No one species dominates and the lake system becomes well-balanced.  

However, things can become unbalanced when invasive plants are introduced. These plants, with few natural predators to check their growth, will often grow very rapidly and attempt to overwhelm the lake. They then drop tons (literally tons!) of leaves into the water as part of their growth and development process. The leaf drop starts building muck on the lake bottom and decreasing oxygen. Furthermore, these overgrown plants block sunlight that is required by native submersed plants and algae, both of which release oxygen as part of photosynthesis. As native plants and algae decline, oxygen in the water decreases further, while the invasive plants are growing at full speed and continue to drop leaves. This process quickly leads to excessive muck and conditions that nobody wants on their lake.  

How can we prevent excessive muck development?

One of the best ways to promote a lake with a healthy level of organic matter is to keep invasive plants at a manageable level. By preventing the overgrowth of invasive plants, organic matter deposition is reduced, the water remains open and well-oxygenated, and critters that live in and consume the organic matter remain active. This restores the balance of the lake and creates a diverse system that supports a wide variety of plant and animal life.  

One of the best ways to promote a lake with a healthy level of organic matter is to keep invasive plants at a manageable level.

Doesn’t spraying herbicide for plant management create more, and possibly toxic, muck?

It stands to reason that spraying invasive plants, and killing them in one fell swoop, would simply accelerate the muck problem. But there are a couple of things to consider before discounting herbicides altogether. 

  1. Invasive plants are dropping leaves every day. If that plant is sprayed, 100% of the plant will drop to the bottom. However, water hyacinth has been documented to drop 60% of its leaves every month. If that plant is allowed to persist for five months, it can theoretically drop 300%, or three plants worth of biomass, over that time period. So timely spraying, and stopping future leaf development/drop, reduces overall muck biomass. 
  2. Waiting to manage “until there is a problem” will create more muck. Allowing invasive plants to proliferate to crisis levels before action is taken means there will be a significant amount of organic matter dropping at one time and this is negative for a number of reasons. However, proactively managing to keep the invasive plant populations low, prevents mass decay of organic matter while keeping the water open and well-oxygenated.  
  3. Herbicides do not create “toxic” muck. All herbicides are required to pass hundreds of tests before the EPA will approve them for use. One of these tests ensures that the herbicide breaks down and dissipates in aquatic environments. After the herbicide is sprayed, sunlight and/or microbes in the water will cause that herbicide to break down and become inactive in the environment very soon after application.  


Muck is natural and necessary for a healthy lake, but too much muck shifts the lake to an unhealthy balance of low oxygen and stressful conditions for aquatic wildlife. Therefore, it is important to manage these lakes to prevent plant overgrowth and excessive biomass production/loss. The best way to do this is by proactively managing invasive plants and encouraging a wide diversity of native aquatic species. Doing this will provide a proper balance in the lake that benefits not only our aquatic friends, but our human friends as well.  

Learn More About Florida’s Lakes

To learn more about Florida’s lakes, check out our podcast, “Working In The Weeds,” where we talk about all things aquatic and invasive plants. In our “Florida Lakes and Landscapes” episode, we discuss how Florida lakes are created, what makes a lake “healthy,” and what makes Florida’s environment prone to invasive species. Subscribe to our podcast for more episodes on all things invasive and aquatic plants.

This blog post was written by Dr. Jason Ferrell, UF/IFAS CAIP director and professor. Questions or comments can be sent to the UF/IFAS CAIP communications manager at caip@ifas.ufl.edu. Follow UF/IFAS CAIP on InstagramFacebook, and TwitterSubscribe for more blogs like this one. 

UF/IFAS Center for Aquatic and Invasive Plants. Turning Science Into Solutions.

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Posted: July 14, 2023

Category: Conservation, Invasive Species, Natural Resources, UF/IFAS, UF/IFAS, UF/IFAS Extension, UF/IFAS Extension, Water
Tags: Aquatic Invasive Plants, Aquatic Plant Management, Center For Aquatic And Invasive Plants, Lake Muck, Natural Resources, UF/IFAS CAIP, Water Quality

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