Fast growing grass
This appears to be yellow nutsedge (Cyperus esculentus). Yellow nutsedge is a perennial sedge native to Michigan that reproduces by rhizomes (underground stems), tubers, and seed.
Late spring/early summer is the ideal time to control yellow nutsedge. At this time yellow nutsedge is young, actively growing, and most susceptible to herbicidal control. As the summer progresses, the nutsedge becomes more mature and begins to form seedheads. At this time it is very difficult to control.
Yellow nutsedge typically thrives in saturated soils, so reducing the amount of water in this area should help alleviate the problem. Nutsedge is difficult to control culturally because it produces numerous tubers that give rise to new plants. Pulling nutsedge often increases the number of plants because dormant tubers are activated. However, small stands of nutsedge can be controlled by persistent pulling which eventually depletes the underground reserves.
Herbicides with the active ingredient sulfentrazone (e.g. Ortho Nutsedge Killer for Lawns) are effective in controlling this species in lawns. As with any pesticide application, it is important to read and follow all labeled instructions to ensure maximum efficacy and personal and environmental safety. Repeat applications may be necessary.