Clemson Extension Forestry and Wildlife

Summertime Pond Problems

Warm water is something people look forward to in the summer for fishing, boating, swimming and more. Warm water also contributes to many common pond problems in the summertime. We will cover the 4 most common summertime pond issues and what can be done to lessen their impacts. 

Excessive Weed Growth

Plants in the water are not inherently bad. In fact, a healthy pond should have some aquatic plant growth. When weeds begin to impede water flow, cover more than 20% of the surface of the water, or start to grow rapidly, they can become a problem. This is a common summertime problem because longer days with more sunlight can encourage the growth of aquatic weeds. Excessive nutrients like phosphorous and nitrogen from the surrounding watershed and warm water temperatures can combine with the sunlight to make previously manageable levels of aquatic plants grow out of control.

Pond covered in green floating weeds

Excessive weed growth is a common problem in ponds in the summertime. Photo credit: Tancey Belken, Clemson University.

There are multiple options of control for pond weeds. Mechanical control includes practices like raking or seining. It can be expensive or labor intensive but can be appealing to some landowners who do not want to use other control methods. Biological control consists of practices like using triploid grass carp to manage weed growth. Stocking rates and sizes vary depending on the pond and the severity level. Certain plants are more likely to be controlled through biological control than others. Finally, there is chemical control, which is using an EPA-approved aquatically labeled herbicide. The first step with chemical or biological control is accurately identifying the nuisance weed. After you identify the weed and determine how much needs to be controlled, you can select an herbicide labeled for controlling the weed in question. Anytime you apply herbicides, by law, you must follow the label directions.  

For more information on aquatic weed control, visit the HGIC Factsheet on Aquatic Weed Control.

Harmful Algae Blooms (HABs)

Harmful algae blooms, or HABs are a hot topic in the news each year. Harmful algae blooms are when certain species of algae grows to excessive levels and can cause foul taste or smell and even produce toxins that can be harmful to humans and other animals. One type of HAB involves cyanobacteria, a type of blue-green algae that causes the water to turn bright green or blue green.

The risk for HABs increase when specific conditions are met. Risk increases when water is warm (usually above 77°F), the pond is receiving high intensity sunlight, the water is slow-moving or stagnant, and the pond has elevated nutrient levels. Heavy rainfalls after a long drought can also result in a harmful algae bloom, when nutrients from the surrounding landscape are washed into the pond.

Pond with green and reddish film on top of it.
Harmful Algae Blooms (HABs) can appear bright green, or reddish brown. Photo credit: Tancey Belken, Clemson University.

Like aquatic weeds, algae are necessary components in aquatic environments. It is the base of the aquatic food chain and has an important role in improving dissolved oxygen when algae is at a healthy level. However, during an algae bloom, decomposition can cause a large drop in dissolved oxygen. Not all species of algae can create a harmful algae bloom or release toxins. Signs of a HAB include a bright green film on the water, scum, foam or thick layers of floating algae, or even red patches of algae. The water can appear green, blue green, or red, but sometimes the algae is not visible. In the case of a possible algae bloom, keep all people and animals out of the water. Do not use it for livestock or crop irrigation. You can send a sample of the algae to the Clemson Plant and Pest Diagnostic Clinic to identify the type of algae, but they do not test for toxins.

The most effective methods to prevent harmful algae blooms are to prevent stagnant water by using an aerator in the pond to keep the water moving and reduce the amount of nutrients that wash into the pond. This can include soil testing to prevent unnecessary fertilization in the yard, preventing livestock from swimming in the water, and deterring geese from residing in the pond.

To learn more about prevention and treatment, visit this HGIC Factsheet on Cyanobacteria.


When ponds are deep and temperatures are high, the water can stratify, or form layers of water with different temperatures. The cool water and warm water separate, with cool water sitting on the bottom of the pond and hot water at the top of the pond. In between those two layers is a warm layer of well oxygenated water where the fish will gather, called the thermocline. This nice separation of layers can be disrupted in an event called a turnover.

A turnover happens when the stratified layers in the pond suddenly mix and the dissolved oxygen level in the water drops. The mix happens when there is a sudden change in weather, like a large rain event, heavy wind, or cold front. The fish clustered in the thermocline suddenly lose the well oxygenated water and some will go to the surface of the water to “gulp” air to stay alive. If the fish are not able to breathe, they will die. This event is called a fish kill, and large fish are normally more susceptible than small fish.

graphic depicting a powered device at the bottom of the pond generating oxygen
Bottom diffusers circulate water through the entire water column. Graphic by Becky Davis, Clemson University.

The most common time of year for a turnover is late Summer and early Fall, but dissolved oxygen issues can happen any time of year. The most effective way to prevent stratification and improve dissolved oxygen levels is to keep the water moving from top to bottom by using a bottom diffuser. A continuously running bottom diffuser will aerate the water by keeping it moving and will pull the water from the bottom and push it to the top, preventing the water from ever stratifying.

For more information on Turnovers, visit the HGIC factsheet on Pond Turnovers.

Low Water

It is common for water levels to drop in the Summer. Hot water and strong sunlight lead to increased water loss through evaporation. The impacts are even more noticeable during times of drought. Some ponds receive most or all their water from rainfall and runoff; without it, the levels can drop rapidly. Other ponds may be supplemented from surface or groundwater, in which case the loss of water may not seem as rapid.

If water levels drop significantly, the pond owner may need to harvest fish to reduce the demand for oxygen in the water that is left. The alternative is to add an aerator to the pond to introduce more oxygen into the environment and reduce stress on the fish.

You do not want to add water from a well to bring the water level back up. Well water will likely have a different temperature and/or pH and can shock the fish, killing some. Adding water that is a different temperature than the pond can also lead to stratification, or layers of different temperatures and oxygen levels forming. A change in the weather can force the pond to turnover and cause a fish kill.

Lower water in the summer is something that can be expected. The most effective course of action is to aerate the water that is left.


Tancey Belken, Cooperative Extension, Forestry and Wildlife Agent

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