Positive cytology for aspergillosis in my Germany shepard's lungs. This patch...
Our plant pathologist looked at your photo and says it is, indeed, algae. It often occurs in areas of yards that stay damp.
Aspergillis is a fungus and would grow on organic matter, not soil.
We recommend that steps be taken to dry up the area by regrading, improving air circulation and sunlight, and solving any unusual sources of water.