There are three types of filters that can help keep a backyard pond beautiful and healthy: biological, mechanical, and chemical filters. Each has a different purpose. Pond skimmers are a type of mechanical filter that grabs leaves and other debris off the surface of a pond. Other types of mechanical filters strain out suspended particles.
Pond skimmers are an important element of backyard ponds, since they keep ponds looking clean. Water features covered in debris and leaves are also unhealthy, and they can create an unsafe environment for fish and water plants. If a pond isn't skimmed regularly, unwanted elements eventually sink to the bottom, decay, and create gases.
These devices are designed to work with other types of filters, as a sort of pre-filter that removes the larger elements such as floating leaves, which would clog other types of biological or chemical filters. These same floating leaves would also clog the pump. Many skimmers are creatively designed to fit with a pond's design. Some may have an artificial rock or natural-looking cover over the top. Some sit outside of the pond and can even be covered up by garden plants or bushes.
Pond skimmers are an important for ponds, since they help keep them clean, and they work hand-in-hand with filtration and pumping systems. They are easy to install and can typically easily be hidden from view. Skimmers should be positioned at the opposite end of a waterfall, if a pond has one; this will help provide for proper circulation throughout the pond.
The the lid of the skimmer is usually the only part that is on the surface; the rest is typically buried underground. When digging the hole for the skimmer, it's important to make sure it fits tightly, so it will not settle in later and become too deep. It must be positioned so that the water level is accurate and the water flows in to the filter at the proper rate.