Fungus or Algae?

Fungus or Algae?
As a Master Garden volunteer, I answer horticultural requests phoned into the local extension office. I worked the phones today. There is usually a trend in the questions depending on the time of year. Now the questions are moles, voles, when to plant and moss. One man complained that he had a fungus or algae in his lawn. Want to bet it was moss? He's bringing in a sample.