lawn getting large yellow patches ????

Our lawn is getting large areas of yellow.
Never had a problem before.I don't use any chemicals no idea what it is or how to treat it.

Does anyone else have this problem ?

 

That would seem unusual considering we have had a wet August when most of the lawns have greened up after the earlier hot weather.

A photo might help up see how bad the problem is.

 

It is the grass itself what is turning a bright yellow but in some areas it is where we had fungi growing earlier on.