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How to Get Rid of Lake Sludge and Algae

    Green water, floating gunk, mushy slime between your toes … None of these things make for a pleasant time in your lake or farm pond.

    Lake sludge and algae are a natural byproduct of your pond’s biological processes. You’ll likely always have a little bit of muck and stringy algae – and that’s OK! When these issues get out of hand, though, it’s time to take steps to control them.

    Lake sludge, muck and algae can usually be treated with a combination of aeration and nature-safe water treatments. Keep reading to learn more about how sludge and algae end up in your pond – and some of our favorite tricks for keeping them under control.

    (By the way – the tips below are specific to larger bodies of water, like lakes and farm ponds. For smaller backyard water gardens, check out our Ultimate Guide to Clear Pond Water.)

    At a Glance: How to Treat Lake Sludge, Muck & Algae

    • Muck and sludge are the result of organic debris decaying in the low-oxygen bottom layer of a lake or farm pond. Algae, meanwhile, feeds off excess nutrients in the water.
    • The first step to reducing muck and algae is to add bottom-diffused aeration.
    • Beneficial Bacteria and Sludge Remover treatments – alongside Treatment Booster Packs – help to further reduce muck and algae and prevent future buildup.

    What Causes Lake Sludge and Algae?

    Lake sludge and algae are two of the most common issues we hear about from lake and farm pond owners.

    While they are separate issues with different causes, they can often be treated with the same combination of aeration and natural water treatments.

    Sludge & Muck

    Sludge or muck is simply organic debris that has decayed at the bottom of a lake or pond.

    Anything that can break down in the water will eventually become muck. Common sources include leaves, fish waste, uneaten fish food, dead algae, weeds, grass clippings and waste from waterfowl. While we would ideally want to prevent this debris from ending up in the water in the first place, nature will eventually do its thing – especially in unfiltered farm ponds and large natural lakes.

    Deep water can further aggravate muck issues. Over time, unaerated ponds stratify into two layers: an oxygen-rich layer near the surface, and a low-oxygen layer on the bottom. Aerobic beneficial bacteria can’t survive in this low-oxygen environment – meaning they can’t do their job of helping to break down debris. Without good aeration, inches or even feet of muck can build up quickly.

    Muck and sludge is unpleasant to look at and even worse to walk in as it squishes between your toes. It can also create an odor like rotten eggs as the organic material decays.


    Algae are plant-like organisms that live in water. While many kinds of algae exist, we typically worry about two kinds in lakes and farm ponds: single-cell algae and string algae.

    Single-cell algae turn water pea soup green. They’re too small to pick up with your hand, but they can make a pond so green that you can’t see far below the surface. String algae, on the other hand, is the filamentous green gunk that clings to rocks or floats on the water’s surface. We often see ponds with crystal-clear water, but an abundance of string algae.

    Both types of algae are byproducts of your pond’s nitrogen cycle. As organic debris breaks down, it gives off ammonia. Bacteria convert this ammonia into nitrites, then other bacteria convert those nitrites into nitrates. Those nitrates then become food for aquatic plants.

    Algae outbreaks occur when something disrupts this cycle. In a single-cell algae outbreak, the pond doesn’t have enough bacteria to break down the nitrites, which then become a food source for the algae. String algae, meanwhile, feed on excess nitrates that aren’t being consumed by plants.

    Algae is rarely dangerous. Your pond will likely always have a little bit of algae, which will provide a source of food for fish and other critters. Too much of it, though, can look unsightly. Algae can also contribute to muck as it dies and sinks to the bottom of the pond.

    How to Reduce Lake Muck and Algae

    Step 1: Increase Aeration

    The most effective way to reduce algae, muck and other problems in a lake or farm pond is to increase aeration. And the best way to increase aeration is to install a bottom-diffused aeration system.

    Lake and farm pond aerators function in much the same way as the ones used in smaller water gardens. The heart of the aeration system is a compressor connected to a power source. This compressor pushes air through self-weighted airline, which goes into the water and carries the air to diffusers in the middle of the pond. The diffusers then push out oxygen that bubbles up to the water’s surface.

    Without oxygen, your pond will go into an anaerobic (low-oxygen) state where only anaerobic bacteria can colonize. Anaerobic bacteria are not as efficient at breaking down organic material as their aerobic counterparts, and they produce gas that makes your pond smell like rotten eggs. When you add aeration to your pond, you create an oxygen-rich environment where the good aerobic bacteria can thrive and go to work breaking down sludge.

    Aeration isn’t just good for reducing muck. With fewer nutrients in the water, algae lose their source of food and ultimately starve.

    Aside from the benefits to your pond’s appearance, aeration will also create a healthier environment for fish. Without aeration, ponds undergo a phenomena called turnover in the fall and spring. Remember those two layers of water, with the low-oxygen water on the bottom and oxygenated water on top? Those layers also differ in temperature for most of the year. During the change of seasons, though, the temperature of the upper and lower layers equalizes, causing the low-oxygen bottom layer to mix with the more oxygenated upper layer. 

    Turnover brings all those rotten egg smells to the surface and, worse still, can suffocate fish. This problem is especially bad in ponds that had frozen over in winter, causing bad gases to become trapped under the ice.

    A good aerator for a lake or farm pond is not cheap – but if you want to enjoy your pond and keep fish healthy, it is well worth the investment.

    Step 2: Add Regular Treatments of Bacteria & Sludge Remover

    Water treatments for lake sludge and algae come in two forms: proactive and reactive. Reactive treatments like algaecide kill algae, but they don’t remove the excess nutrients that let the algae grow in the first place. Similarly, muck can be manually removed from a pond (this is called dredging), but it won’t prevent future muck buildup.

    We prefer to use water treatments that work with nature to balance the pond or lake ecosystem. The following three products provide a long-term solution for muck and algae, saving you money in the long run. 

    By the way – proactive water treatments are at their most effective when used in addition to a bottom-diffused aeration system. While they will do some work on their own if you can’t afford aeration right away, your pond will be at its healthiest if you combine the two methods.

    Lake Sludge Remover Packs

    FREQUENCY: Once per month when water is warmer than 45 degrees
    APPLICATION: Toss the water-soluble packs directly into the water. One pack treats up to 250 square feet.

    Lake Sludge Remover packs use a mix of bacteria, carbon and macrobiotics to reduce pond muck. The packs can remove up to 3 inches of muck per month and can be applied to lake bottoms, beach areas and shorelines. They are safe for fish, plants and animals when used as directed.

    (Only use Lake Sludge Remover in large bodies of water like lakes and farm ponds. For smaller water gardens, we recommend this Sludge & Filter Cleaner.)

    Lake Bacteria Packs

    FREQUENCY: Once per month when water is warmer than 45 degrees
    APPLICATION: Toss the water-soluble packs directly into the water. Four packs treat up to 1/4 acre.

    Lake Bacteria Packs restore the ecosystem in lakes and large ponds, starving algae and keeping water clean, clear and healthy. The easy-to-use water-soluble packs dose the water column evenly, making it easy to treat hard-to-reach areas.

    This treatment is fortified with prebiotics to improve probiotic growth and enhance water quality. It will not cause the “floating sawdust” effect often seen with other lake bacteria treatments. Lake Bacteria is safe for fish, plants and animals when used as directed.

    (Only use Lake Bacteria in large bodies of water like lakes and farm ponds. For smaller water gardens, we recommend this Beneficial Bacteria.)

    Lake Treatment Booster Packs

    FREQUENCY: Once per month at the same time as Lake Bacteria and Lake Sludge packs
    APPLICATION: Toss the water-soluble packs directly into the water. One pack treats up to 250 square feet.

    Lake Treatment Booster Packs use a blend of elements to add oxygen to the water to accelerate nutrient uptake, sludge digestion and bacteria growth. The water-soluble packs dose the sludge layer directly and make it easy to spot treat or treat hard-to-reach areas.

    This specially designed treatment is great for use in non-aerated or highly eutrophic (nutrient-rich) bodies of water. Lake Treatment Booster Packs are ideal for use with Lake Sludge Remover Packs, Lake Bacteria and Lake Phosphate Binder Packs. Safe for fish, plants and animals when used as directed.

    (Only use in large bodies of water like lakes and farm ponds. Treatment Booster is not necessary in smaller water gardens.)