Anyone know what this is in my grass?someone told me it could be from overwatering. It’s spongy like 

What are we looking for? 

The brighter green patches. I have it all over mainly In the shady areas of the yard. Both front and back

Looks like uneven fertilizing, or those spots are the first to show they need more, like the next application. Suppose it could also be any of the myriad of lawn problems that we all fight every year, bugs, fungus, etc etc.

 

if I look out at my back lawn, I have dark and lighter areas, although not in lines like your looks to be.

  
 

if you have a lan service for fertilizer, call and ask them. When I had one if I called they’d send someone out to look it over.

Need some better pictures. Is it a grass/plant?  If so, is the grass quite different to the rest of the grass around?

 

The color has the characteristic color of poa.  Poa is a family of grasses that are an obnoxious weed to most people.  There are two main ones that most people experience. Both are kinda like green vs dark green grass. One version dies when the temp goes up and leaves a brown bare spot. 

You said it’s spongy. Is it moss growing under the grass? That’s usually a symptom of soil that gets a little too much water and shade. 
 

Other wise I’d agree with @padlin, possibly some burns from uneven fertilizing. 
 

Another thing on the “sponginess’s of it. One of my lawn customers last year had a big patch of grass that was bulging and very jiggle and bouncy. Took my pocket knife and stabbed the bulge in the middle and gallons and gallons of water drained out. No more spongy bulge. So if you can feel water underneath, try stabbing it and letting some water drain out.