Algae in Ponds

Ponds are wonderful landscape features to have on your property. These bodies of water add beauty and value. However, ponds can have issues.

Ponds can have many problems. Lawn care has become more intense over the years with more frequent mowing and applications of fertilizers. Too many nutrients entering the ponds from stormwater runoff carrying fertilizers or blowing grass trimmings or leaves into ponds can cause algal blooms.

Sometimes a pond can get too shallow over the decades of its existence though sedimentation allowing sunlight to reach the bottom and causing plants and algae to grow. Sometimes pond owners remove the natural plant growth around the edges of the pond allowing light to shine on the shallow water at the pond's edge which encourages algae. If a pond is too warm and too clear plant and algae growth can occur around the edges. Pond algae is worse these days with our warmer winters, older ponds that have gotten shallow, intense lawn care practices and resident waterfowl spreading algae and other weeds.

Healthy ponds should be deep and have steep banks under water. Ponds should also have a healthy murkiness. The healthy dark murky color of ponds is caused by a phytoplankton bloom. Mowing the edges of the pond increases weeds by allowing sunlight into the pond which feeds plants and heats water. Grass clippings that enter the water can provide nutrients which feeds pond algae and weeds. If your pond is too clear and too shallow around the edges, algae and plant growth can occur.

Phytoplankton are microscopic creatures that grow in nutrient rich water. Nutrients in water get diluted when we have rainy summers like the one from this last summer or if the pond source is an underground spring. Extremely clear ponds can grow weeds and algae.

If you have algae in your pond, you should try multiple approaches to get rid of it. 

First, remove all the plants and algae that you can with a rake. Get a hard-tined rake, drill a hole in the handle, and tie a rope. Toss out the rake and pull it in with the rope. This is laborious but can reduce the amount of algae in your pond considerably.

Second, deepening the edges of an existing pond to an incline of 2:1 helps control algal growth. A 2:1 slope lessens the amount of shallow areas penetrated by sunlight and limits algal growth. Sunlight that penetrates and touches the pond bottom less than 18" deep can lead to plant and algae growth.

Mowing around ponds allows sunlight to enter water. Grass clippings that enter the water can provide nutrients which feeds pond algae and weeds. Cease mowing operations around the pond to allow regrowth of native plants and improve pond health. A healthy plant border around the pond will be a refuge for wildlife such as aquatic invertebrates, amphibians and baby fish as well.

Lastly, algaecides are chemicals that kill algae in water. You buy algaecides locally at several local farm stores including Southern AG or online. In the mountains, be sure to test your pond's pH prior to using copper products.

Some pond owners such as HOAs find it easier and more effective to hire a pond contractor to manage their pond.

Finally, here is our pond management publication if you would like to learn more about caring for your pond.