During extended periods of wet weather, deposits of a slimy substance can begin to appear on your grass, and when the temperature begins to rise in the summer these wet deposits will dry out and form dusty spores on the grass. Luckily these spores are only able to live on dead and decaying plants so they shouldn’t cause you too many issues. They may block sunlight to healthy grass shoots resulting in areas of your lawn turning yellow (in a similar manner to leaving a paddling pool or other object on the lawn for a few days), if this happens it’s simple enough to simply brush or rake the lawn to dislodge the spores.
Interestingly, slime moulds are not fungus but ‘protist’ a unique type of organism that doesn’t fit in with usual classifications of species, and yet they are found everywhere! Scientists have observed the behaviour of slime mould and found it is able to ‘navigate’ to a food source, even moving around obstructions in the process. It’s almost as though it has a brain, though of course it most certainly does not!