Lake Management Guide

Lake management is a challenging world filled with acronyms, jargon and complex science that can present an even bigger headache than the problem you’re trying to resolve. This user-friendly guide breaks down commonly used lake management terms, so you have all you need to know to kickstart your lake management plan for a healthy water body.


Actinomycetes are an aerobic type of filamentous fungi-like bacteria that emit toxins associated with cyanobacteria – also known as blue-green algae. These toxins are also responsible for the tell-tale taste and odour of cyanobacteria as they are produced by digesting dead cyanobacteria. Circulating a lake system with other types of bacteria can lower the concentrations of actinomycetes as anaerobic bacteria quickly outcompete them.

Activated carbon

Drinking water plants use activated carbon to remove impurities that affect the water’s taste, odour and colour, alongside toxins and other harmful contaminants. Activated carbon is usually comprised of wood-based carbon and resembles crumbled charcoal. It is commonly used in two primary forms: granular activated carbon (GAC) and powdered activated carbon (PAC).


Aeration systems are typically designed for “hypolimnetic aeration” and are comprised of a compressor on shore, air pipes laid in deep water at the bottom of the lake, and air-bubble outlets (diffusers) mounted on the pipes. The purpose of a compressor is to prevent phosphorus from the lake sediment being (internal loading) by maintaining the oxygen demand of deep water. It does this by preserving the lake’s natural stratification and meeting its oxygen demand by providing oxygen from the atmosphere.


Algae are simple one-celled plants that are typically very small in size (microscopic), meaning they are not visible to the naked human eye. They are a diverse group of organisms that produce energy via photosynthesis. Algae do not possess a central vascular system for either respiration or nutrient flow. You can learn more about different types of algae and their characteristics in our guide.


Commonly referred to as blue-green algae, cyanobacteria are a phylum of bacteria that can generate many problems for aquatic environments due to their ability to produce toxins. More than 70,000 species of algae are known to science, but less than 100 of them are classified as cyanobacteria. Harmful cyanobacteria blooms pose a risk to human health, water quality and aquatic life. You can learn more about cyanobacteria in our guide to cyanobacteria blooms.


Cyanotoxins are the toxins produced by cyanobacteria that harm humans, wildlife and the wider environment. While cyanobacteria are present in almost all environments, their toxins in high concentrations can be hazardous to life. The build-up of cyanotoxins has been associated with skin problems and many neurological diseases. Experts estimate that there are over 100 different cyanotoxins, each with its own management requirements. Key cyanotoxins to be aware of are hepatotoxins (affecting the liver), neurotoxins (affecting the nervous system), and dermatoxins (affecting the skin). Prepare yourself for the signs of harmful algal blooms in this blog.


Also known as ‘common water fleas’, daphnia are small zooplankton crustaceans that live in freshwater environments such as lakes and wastewater ponds. Daphnia are thought to be the most important zooplankton and are an essential link in the food chain as they eat algae and, in turn, are eaten by fish. Daphnia are large enough to ingest green algae and diatoms, but not big enough to eat cyanobacteria. The faecal matter they produce is an essential source of organic carbon for bacteria. Daphnia are also imperative to maintaining water quality as every day; a single daphnia can filter the same volume of water as a small office. These planktonic crustaceans are most active when the water temperature is over 50˚F (10˚C).


Diatoms are a type of microscopic cold-water algae that have a hard exoskeleton and are usually brown. Because of their brown colouration, a high concentration of diatoms typically gives a brown tint to lake water in the spring and fall. Diatoms are not mobile and so can only move with the water currents. They are known as phosphorus scavengers and are most productive in lake mixing conditions during the fall and after ice out in the spring. Throughout this period, they frequent the entire water column as they absorb all the phosphorus they need.


Dinoflagellates are characterised by two flagella that allow them to move through the water. They get their name –‘dino’ – from their armour-like exoskeleton that protects them from predators. These photosynthetic algae can produce strong toxins that kill fish, especially in estuarine and marine waters. They are commonly associated with lethal “red tides”, and like cyanobacteria, dinoflagellate blooms are considered HABs (harmful algal blooms).

Dissolved Oxygen

Dissolved oxygen (DO) is the quantity of oxygen present in the water. Water bodies absorb oxygen from the atmosphere, and aquatic plants’ presence also increases the oxygen concentration in the water. Running water, mixing, or wave action, dissolves more oxygen than the still water of a pond or a lake.

Similar to land animals, all aquatic animals require oxygen to breathe. When dissolved oxygen concentrations are low (hypoxic), or there is no oxygen present (anoxic), there is a risk of death, such as fish kills. This typically happens when excess organic materials, such as large algal blooms, are decomposed by microorganisms. Throughout this decomposition process, dissolved oxygen in the water continues to be consumed. While dissolved oxygen levels naturally fluctuate with the seasons, when they drop significantly, some sensitive animals may migrate from the area, decline in health or even die, so it is vital to monitor dissolved oxygen levels continually.


Eutrophication is characterised by an entire body of water becoming gradually more enriched with nutrients – primarily with nitrogen (N), phosphorus (P) and organic matter. Cyanobacteria blooms are a symptom of eutrophic lakes by mid or late summer if careful monitoring and management plans are not initiated to curtail cyanobacteria growth. You can learn more about eutrophication in our nutrient pollution article.

Fish kills

An event is classified as a ‘fish kill’ when an unusually high number of fish die within a short period. They are a symptom of harmful algal blooms, such as during summer cyanobacteria blooms. Fish kills may also be triggered by bacterial decomposition caused by a mass algae die-off as dissolved oxygen concentrations are driven down. Abnormal weather conditions, such as a summer storm, may also lead to a fish kill event as unusual mixing brings anoxic water from the bottom to the top. Fish kills can also occur at fall turnover in a eutrophic lake when the anoxic hypolimnion mixes throughout.


Flocculants are substances (usually chemicals) that encourage the clumping of fine particles into larger particles to create a floc that floats to the surface or settles on the bottle. They are mainly applied to lakes to draw phosphorous out of the water and settle on the lake’s bottom. Alum, chitosan, various bentonite, lanthanum and other clays are the most commonly used flocculants for lakes. Learn more about flocculants in our blog.

Gas vesicles

These hollow structures are unique to cyanobacteria cells and allow them to adjust their buoyancy and position in the water column. Cyanobacteria typically move up toward the lake surface in the early hours of the day to maximise their exposure to sunlight and atmospheric carbon dioxide and nitrogen. This comes as a cost to other algae below them in the water column as they block light, preventing the algae from photosynthesising. Cyanobacteria then move down into more nutrient-rich waters in the evening. You can learn more about cyanobacteria and gas vesicles in our blog.


Geosmin is a compound produced by cyanobacteria that creates an “earthy” taste and odour in the water. You may be familiar with this smell as it is the same odour released from terrestrial garden soils when tilled.

Harmful Algal Bloom (HAB)

Harmful algal blooms are usually a proliferation of cyanobacteria, also known as blue-green algae, in freshwater systems. In the marine environment, harmful algal blooms (“red tides”) are typically caused by toxic dinoflagellate. HABs are triggered by an influx of nutrient enrichment in a water system and are characterised by eutrophic waters. In recent years, they have become more common and more severe.

Internal Loading

Internal loading refers to the circulation of phosphorous (P) in a freshwater ecosystem released from the sediment. When cyanobacteria (blue-green algae) penetrate this nutrient cycle, a toxic, harmful algae bloom (HAB) event will likely occur on the lake for the remainder of the summer. In this event, flocculants can be applied to a lake to reduce internal loading as the two primary nutrients that trigger blooms are phosphorous (P) and nitrogen (N). Read more in our nutrient pollution article.

Lake Restoration

Lake restoration is costly and time-consuming as it can take many years to obtain the required permissions and implement an effective plan. A lake restoration plan usually aims to make a lake safe or aesthetically pleasing by reducing algal blooms. Many lake restoration plans fail as they lack sufficient access to funding or management tools that effectively lower algae presence. Obtaining at least five quotes for consultant work and a performance warranty is highly advisable to protect the interests of lake owners and the project.


Growing in or near the water, macrophytes are large aquatic plants that are more complicated than algae as they contain a vascular system for transporting nutrients and water within the plant. Generally, aquatic macrophytes can be categorised into the following:

  1. Emergent aquatic plants: These are rooted in the lake bottom, with their leaves and stems extending above the water surface. Examples include cattails and bulrushes.
  2. Submerged aquatic plants: These are rooted in the lake bottom and are entirely underwater. Examples include musk grass and pondweed.
  3. Floating-leaf aquatic plants: These are rooted in the lake bottom with their leaves and flowers floating on the water surface. Examples include white water lily and duckweeds.

Importantly, invasive macrophytes are usually lightly-rooted and can spread rapidly throughout the lake ecosystem via fragmentation. While native macrophytes are more deeply rooted, they may be outcompeted by invasive macrophytes. Learn more in our blog.


Manganese can pose risks to human health if it’s in high concentrations. For this reason, many water treatment plants reduce manganese through a process known as oxidation to filter it out. Oxidised manganese is distinctive as it resembles small pebbles with a black tinge that can be easily filtered. However, if manganese concentrations are too high, then the removal system may not be able to handle it.

Manganese presents several challenges to water managers due to its unique chemistry. Experts believe manganese enters a water system through shallow groundwater. Once it is in a lake that lacks a thermocline and experiences mixing across all depths, any manganese that is present will be oxidised across the system. If a lake also experiences issues with iron, then this is a further headache for a water treatment plant.


Mercury is a widespread element and a persistent pollutant that enters aquatic environments through numerous pathways, including mining and other human activities. It is, therefore, unsurprising that it is found in most US lakes. Despite stricter regulations around power plant pollution today, as mercury is a persistent pollutant that remains in the environment and accumulates in food chains long after it was first introduced, it is tough to remove.

Stormwater runoff is a considerable contributor to mercury in rivers and lakes. Although mercury does exist in non-harmful dissolved toxic forms, it is highly toxic in anoxic methylated forms. The US Army Corp of Engineers believes mercury is one of the biggest health problems in US water.

Nonpoint Source

Nonpoint source pollution refers to any source of pollution that flows into a system through an undesignated point. Examples include excess fertilisers, herbicides and insecticides from agricultural land, inflow from groundwater and toxic chemicals from urban runoff. While many watershed protection projects aim to reduce nonpoint source nutrients to prevent cyanobacteria blooms in lakes, unfortunately, virtually no watershed project has ever accomplished this goal. You can find more information on nonpoint source pollution in the  Clean Water Act.


Nutrients are crucial for a healthy ecosystem, but an over or under abundance of nutrients can have devastating ramifications. Carbon (C), nitrogen (N), and phosphorus (P) are the most important nutrients to biotic (living) organisms. Alongside these, others nutrients such as sodium, iron, calcium, silica, and magnesium are also necessary. As the base of the food web, plankton serves as key indicator species of nutrient composition as heterotrophs (animals) that need to eat organic material reflect the content of plants, which are autotrophs and at the bottom of the food chain.


pH is a measure of the acidity or alkalinity of water that uses the concentration of H+ ions and OH-ions. It reflects the chemical conditions of water and is an essential indicator of water quality. Read our guide to pH to learn more.


Phycocyanin is found in cyanobacteria, also known as blue-green algae, where their role is to absorb solar energy for photosynthesis. Phycocyanin presence is a key measure for cyanobacteria within a water body as the chlorophyll-a pigment is found within both green algae and cyanobacteria.


Planktonic is a term used to describe free-floating organisms that are immobile, i.e. not capable of directed movement, within aquatic environments such as lakes and the coast. Plankton is a vital part of aquatic food webs and includes organisms such as green algae and diatoms. Most planktonic organisms are heavier than water but have evolved shapes and other characteristics to reduce their sinking rates so that they can maintain their position in the water column.

Point Source

Point source water pollution is that discharged from a specific location that can be regulated to ensure it has minimal impact on the aquatic environment, such as a river or a lake. Point sources may derive from a municipal wastewater treatment facility effluent pipe. In the United States, point sources are regulated using permits that coincide with the US EPA National Pollution Discharge Elimination System (NPDES). Read our NPDES effluent guidelines article for more information.

Red Tide

Red tide is a form of harmful algal bloom that takes place in the marine and coastal environment, usually near the shore. Their name derives from the toxins that often alter the tinge of the water. Red tides are highly hazardous to the health of people, wildlife and the environment. Unfortunately, they are increasing in frequency and severity.

Retention Pond

Retention ponds are designed to prevent runoff water from reaching a property or a designated water body. Although their water levels may fluctuate, water is usually always within a retention body. That said, dry retention ponds are another tool intended to dry out several days after a rain event due to water escaping via ground infiltration.


Water is a finite resource that is becoming scarcer and scarcer. Urban planners are identifying ways to reuse more wastewater for irrigation, and some cities are doing so by pumping treated wastewater into lakes for storage. This may increase water availability for irrigation, but it poses an ecological nightmare. Wastewater increases the likelihood of a lake becoming anoxic in the summer months. Depending on the nutrient and chemical composition of the wastewater, additional problems may occur for the lake. For example, if aluminium sulfate was used at the wastewater plant to remove phosphorus (P) from the wastewater, the sulfate can form sulfides in the lake. These sulfides then become so concentrated in the lake that algae and other life cannot grow due to the lack of dissolved oxygen. Ultimately this means the lake is at risk of becoming a dead zone with a foul-smelling odour.


Salinity is a measure of the concentration of ions present in water. These ions are typically sodium, potassium, magnesium, calcium, carbonate and silicate. Salinity is referred to as taking three forms: primary salinity, secondary salinity and tertiary salinity. Salinity is imperative for the survival of aquatic flora and fauna; however, hypersaline and low saline environments can harm the health of humans, wildlife and the wider environment.

Ultrasound Technology

Managing algal blooms presents several issues for water managers as many conventional methods pose a risk to the aquatic environment. Ultrasound technology presents a novel way of controlling algal blooms without having a negative impact on the environment. Ultrasound technology is best paired with a robust water quality monitoring programme, and the careful changing of frequencies is essential. Read our blog post about LG Sonic ultrasonic algae control to learn more.

Stormwater Ponds

Stormwater ponds are those that are constructed to reduce the negative implications of stormwater runoff by lowering the concentrations of nutrients, such as nitrogen (N) and phosphorus (P), as well as sediment, oil, heavy metals, and other debris that runs into the receiving stream, lake or ocean. They are an essential part of stormwater management.


Stratification is the separation of water into layers usually dictated by water temperature or density, although other factors like salinity and water pressure also apply. More dense water typically separates to the bottom of a water body, whereas less dense layers drift to the top surface layers.


Total suspended solids (TSS) is an important water quality parameter that managers can use to assess the health of a water body and is listed as a conventional pollutant in the U.S. Clean Water Act. It is commonly used on wastewater samples after undergoing treatment through a wastewater plant. The measurement is of the dry weight of non-dissolved suspended particles in a water sample. In order to obtain this measurement, a sintered glass crucible is used to trap the suspended particles in a filter.


Turbidity is a term used to measure the clarity of the water. Water clarity usually decreases as water becomes cloudier due to the presence of particulate matter suspected in the water. Particulate matter can either be organic, such as a high concentration of algae, or inorganic, such as clay particles. It is ascertained using the amount of light that can penetrate a water sample and measured in nephelometric turbidity units (NTU). The Environmental Protection Agency (EPA) standard for drinking water in the United States is below 5 NTU. All drinking water systems must be fitted with a filter to prevent turbidity from exceeding 1 NTU (0.5 NTU for conventional or direct filtration) in at least 95% of the daily samples for any two consecutive months.


Zooplankton are microscopic animals that live in aquatic environments. They can direct their own movement but are more commonly passively transported by water movement. Healthy zooplankton populations are an indicator of water quality. There are three main groups of zooplankton:

  1. Cladocera: Commonly known as water fleas, these relatively large microcrustaceans are filter feeders that eat algae. Examples include daphnia and alonella.
  2. Copepods: These small crustaceans are found in almost every aquatic habitat on earth and are important biodiversity indicators.
  3. Rotifers: Commonly known as ‘wheel animals’, these microscopic organisms are usually found attached to substrates such as detritus or sediments.