Officers from Natural Resources Wales (NRW) have recently dealt with two major slurry pollution incidents in Carmarthenshire and Pembrokeshire.
They also dealt with a serious diesel spill on a Carmarthenshire farm.
NRW has warned that these pollutants can kill fish and harm birds.
Phil Morgan, catchment coordinator at NRW, said that reporting incidents quickly will help to "reduce the environmental impact".
Guidance has been issued on legally storing silage, slurry and fuel.
Farmers have been urged to store their silage, slurry and diesel appropriately following three major pollution incidents in Wales.