There are a couple of signs that your septic leach field is having an issue:
Your drain field is unusually wet or mushy.
The grass over your field is much greener than that of the rest of your yard.
There’s a heavy sewage odor over your field.
Sewage has started to back up into the house.
Leach field issues can be caused by a number of different things, from tree roots causing damage, to excessive rainfall causing it to overflow. These issues should never be treated lightly, both for the sake of your health and the health of the surrounding environment.