Water features typically use moving water, such as fountains or waterfalls, and they often don't house fish, although some can. Algae can quickly take over the surface of your feature and coat any water-covered surface, so even your kids will think it's yucky. Some algae helps create a natural balance in your water feature, but other types block sunlight and ingest nutrients necessary for other plants to grow or for your fish to thrive, if they live in your water feature. With some persistence, you can control the algae before it takes over.
Locate your water feature where it doesn't receive runoff from your yard. Tall fountains set up off the ground might not have this problem, but streams, ponds and waterfalls placed in low-lying areas can collect rainwater as it runs off. This water carries chemicals used on your lawn, such as fertilizer, which encourages algae growth.
Skim out floating algae with a small-mesh pond net, or get your kids involved in cleaning the water feature. Slide the net into the water outside the algae clump with one side of the net above water, and then move it over the algae to scoop it into the net. Dispose of it in a trash bag.
Add algae-fighting plants to your water feature, if space allows. Some plants ingest more nitrogen than others, robbing algae of this nutrient it needs to flourish. These plants include water pickerel (Pontederia cordata), hardy in U.S. Department of Agriculture plant hardiness zones 3 through 10, and taro (Colocasia esculenta "Black Magic"), perennial in USDA zones 8 through 10. These plants may be considered invasive in some areas of the country, so check your state's invasive species list before adding them to your pond.
Treat your water feature with a copper algaecide. The amount of algaecide you need depends on the water volume moved through your water feature, so check the paperwork from the water feature to determine the volume. Compare that to the manufacturer's chart on the algaecide container to discover how much to add to your feature. Pour the correct amount in slowly along the sides, letting the movement of the water spread it throughout the feature.
Add koi if your water feature it's one that can support fish life. Koi eat string algae, helping keep your water feature clean.