Symploca and Oscillatoria species Algae is composed of single-cell freshwater plants that grow on bare, wet areas of the lawn. Although it does not harm grass, it is unsightly, and is a sign of a thinning lawn. Invaded areas become slippery. Algae live on compacted soil and soil that is high in nitrogen and organic matter. It needs wet conditions to survive. Organic fertilizers encourage algae, especially in the cool seasons.
Reduce soil compaction, improve drainage, and prune nearby trees to reduce shading. Avoid high-nitrogen fertilizers in late fall and winter. Maintain a healthy, vigorous lawn by following proper lawn care practices.