Scrub your birdbath immediately if algae start to grow. Use very hot water and a good scouring brush.
Water in birdbaths should be changed at least every three days, and in warm weather even more often. Algal growth is one issue, but even more urgent and potentially dangerous is the possibility of mosquitoes breeding. The mosquitoes that breed in small stagnant pools, such as rain gutters and birdbaths, are the ones most likely to harbor West Nile Virus, which is dangerous for both humans and birds. The importance of keeping water in birdbaths clean cannot be overemphasized.
Also, providing an aerator or a slow drip from an overhanging bottle will attract a wider variety of birds to your birdbath.
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