This looks like an algae growth in the lawn area.  There may be several reasons you have algae in your lawn which include poor soils, poor drainage, compaction, poor lawn care practices, shade, etc. If you want to get rid of it, you need to correct the conditions that favor its growth.
Look at our website for photos and more information.  http://extension.umd.edu/hgic/algae-lawns

Begin by testing your soil for pH, liming, and nutrient deficiencies.  http://extension.umd.edu/hgic/soils/soil-testing
You may need to increase drainage, aerate if compacted, select shade tolerant
grass species if too much shade, reseed in the fall, etc.

 See our publication for turfgrass maintenance http://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG112_Turf...
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