Some ponds may smell bad due to the buildup of organic matter and other debris, which can cause the growth of bacteria and other microorganisms that produce foul-smelling gases like hydrogen sulfide and methane. These gases are commonly referred to as pond gas or pond muck.
The buildup of organic matter in a pond can be caused by a variety of factors, including excessive nutrients (such as from fertilizer runoff or animal waste), dead plant material, and animal waste. When these materials break down, they can create anoxic (low oxygen) conditions in the pond, which promotes the growth of anaerobic bacteria that produce the foul-smelling gases.
Other factors that can contribute to bad odors in a pond include low water levels, stagnant water, and high temperatures. In some cases, the presence of certain types of algae or aquatic plants can also contribute to bad smells.
To prevent bad odors in a pond, it's important to maintain good water quality through regular maintenance practices such as removing debris and excess vegetation, ensuring proper nutrient balance, and promoting oxygenation of the water through aeration. Proper pond management practices can also help to control algae and bacterial growth and promote a healthy and balanced ecosystem.